ENAMELS 

Robert     D.     Landrum 


GIFT  OF 


ENAMELS 


Robert     D.      Landrum 


FOREWORD 

This  little  book  is  a  collection  of  the  various 
articles  on  Enamel  published  by  the  writer  in  the 
various  technical  journals  to  which  credit  is  given 
with  each  article. 

There  are  also  included  some  tables  of  interest 
to  the  Enameling  industry  and  space  is  provided 
at  the  end  of  the  volume  for  additional  data  of 
this  kind. 

The  book  is  published  for  the  benefit  of  the 

r        Enameling  industry  by  THE  HARSHAW  FULLER 
*     &  GOODWIN  COMPANY,  Cleveland,  Ohio,  and  is 
presented  with  its  compliments. 

Robert  D.  Landrum 
January  1st,  1918. 


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»a  >'i  .„.,* 


CONTENTS 

Page 
I    Enamels  for  Sheet  Steel 7 

II.    The  Function  of  the  Various  Raw  Materials  in  a 

Sheet  Steel  Enamel  15 

III.  Resistance  of  Sheet  Steel  Enamels  to  Solution 

by  Acetic  Acids  of  Various  Strengths 26 

IV.  A  Comparison  of  Ten  White  Enamels  for  Sheet 

Steel 34 

V.    The  Necessity  of  Cobalt  in  Ground  Coat  Enamels 

for  Sheet  Steel 60 

VI.    Methods  of  Analysis  for  Enamel  and  Enamel  Raw 

Materials 70 

VII,    Atomic  and  Molecular  Weights  and  Factors  used 

in  Ceramic  Calculations 101 

VIII.    Cubical  Coefficient  of  Expansion! 106 


ENAMELS  FOR  SHEET  STEEL  *i 


Enamels  for  sheet  steel  are  boro-silicates  of  sodium, 
!  -  "~  and  are,  in  every  sense 

tels  are  so  compounded 
ossy  coating  on  the  sur- 
ch  will  not  be  corroded 
Booking  and  which  will 
;  and  by  rapid  changes 


ise  common  to  cooking 

lltiOn    °f    °ther 


THEHARSHAW  FULLER  a  GOODWINco 

CLEVELAND  ELYR.A  NEW  YORK 


ROBERT  D.LANDRUMCH.E. 

MANAGER  SERVICE  DEPARTMENT  CLEVELAND          icturing  ordinary  glass. 

•  sand  supply  the  silica, 

«aiu.  jLciuopai  aim  ciay,  me  aiumina.  Fluorspar  or  cal- 
cite  is  added  to  supply  the  lime  and  cryolite  to  render 
the  enamel  translucent.  Soda  ash  and  pearl  ash  are 
fluxes  adding  sodium  oxide  or  potassium  oxide  to  the 
product,  and  borax  furnishes  the  boric  anhydride,  which 
adds  many  desirable  qualities,  such  as  greater  ductility 
and  elasticity.  Sodium  or  potassium  nitrate  is  used  in 
white  enamels  and  manganese  dioxide  in  dark  colored 
enamels  as  an  oxidizing  agent.  Oxide  of  cobalt  is  used 
in  enamels  which  come  directly  in  contact  with  the  steel 
and  adds  adhesiveness  to  this  coating. 


For  producing  white  enamels,  oxide  of  tin  is  used; 
for  blue,  cobalt;  for  violet  and  brown,  manganese;  for 
gray,  nickel  ;  for  green,  copper  or  chromium  ;  for  yellow, 
uranium  or  titanium  ;  and  for  red,  iron,  selenium  or  gold. 


*Reprinted  from  the  Journal  of  Industrial  and  Engineering  Chemistry,  Vol.  4. 
No.  8,  August,  1912. 

1  Delivered  before  the  Chemists'  Club  of  Rochester  at  the  University  of  Rochester, 
Rochester,  New  York,  April  1,  1912. 


ENAMELS  FOR  SHEET  STEEL  *i 

Enamels  for  sheet  steel  are  boro-silicates  of  sodium, 
potassium,  calcium  and  aluminum  and  are,  in  every  sense 
of  the  word,  glasses.  Such  enamels  are  so  compounded 
that  they  form  a  homogeneous,  glossy  coating  on  the  sur- 
face of  the  sheet  steel  utensil,  which  will  not  be  corroded 
by  the  acids  or  alkalies  used  in  cooking  and  which  will 
resist  punishment  both  by  impact  and  by  rapid  changes 
of  temperature. 

Although  an  enamel  is  a  glass,  the  fact  that  it  must 
adhere  to  steel  and  resist  the  abuse  common  to  cooking 
utensils  makes  necessary  the  addition  of  other  ingredi- 
ents besides  those  used  in  manufacturing  ordinary  glass. 
In  enamels,  ground  quartz,  flint  or  sand  supply  the  silica, 
and  feldspar  and  clay,  the  alumina.  Fluorspar  or  cal- 
cite  is  added  to  supply  the  lime  and  cryolite  to  render 
the  enamel  translucent.  Soda  ash  and  pearl  ash  are 
fluxes  adding  sodium  oxide  or  potassium  oxide  to  the 
product,  and  borax  furnishes  the  boric  anhydride,  which 
adds  many  desirable  qualities,  such  as  greater  ductility 
and  elasticity.  Sodium  or  potassium  nitrate  is  used  in 
white  enamels  and  manganese  dioxide  in  dark  colored 
enamels  as  an  oxidizing  agent.  Oxide  of  cobalt  is  used 
in  enamels  which  come  directly  in  contact  with  the  steel 
and  adds  adhesiveness  to  this  coating. 

For  producing  white  enamels,  oxide  of  tin  is  used; 
for  blue,  cobalt;  for  violet  and  brown,  manganese;  for 
gray,  nickel ;  for  green,  copper  or  chromium ;  for  yellow, 
uranium  or  titanium ;  and  for  red,  iron,  selenium  or  gold. 


*Reprinted  from  the  Journal  of  Industrial  and  Engineering  Chemistry,  Vol.  4. 
No.  8,  August,  1912. 

1  Delivered  before  the  Chemists'  Club  of  Rochester  at  the  University  of  Rochester, 
Rochester,  New  York,  April  1,  1912. 


Enameliig^k  still  held  as  a  secret  art,  and  the  for- 
mulas are  carefully  guarded.  Most  companies  allow 
very  few  visitors  to  go  through  their  plants  and  some 
keep  their  employees  in  ignorance  by  various  schemes. 
In  one  American  works,  each  of  the  enamel  raw-materials 
is  given  a  number.  They  are  ordered,  shipped,  kept  ac- 
count of,  and  stored  under  their  respective  numbers,  and 
only  those  in  authority  even  know  what  materials  are 
used.  In  this  same  factory,  employees  of  one  department 
are  not  allowed  in  another  and  after  being  employed  in 
one  department,  a  man  is  barred  from  employment  in  any 
other.  Some  works  have  the  formula  for  each  enamel 
divided  into  two  parts,  one  of  which  is  mixed  by  one  man, 
the  other  by  a  second,  and  certain  proportions  of  each  are 
then  mixed  together  by  a  third  man.  In  practically  all 
enameling  works,  the  materials  are  weighed  on  a  scale, 
the  beam  of  which  is  hidden  from  the  laborers,  who  are 
also  generally  of  foreign  birth  and  are  changed  fre- 
quently. 

The  "Black  Shape." — The  sheet  steel  which  is  used 
for  enameled  ware  is  as  nearly  as  is  possible  free  from 
carbon,  silicon,  sulphur  and  phosphorus,  and  its  manga- 
nese content  is  generally  about  0.2  per  cent.  These  sheets 
come  in  squares  and  oblongs  from  27  to  20  gauge  and  are 
circled,  stamped  and  spun  with  as  little  heat  treatment 
as  possible  and  with  the  use  of  a  lubricant  that  can  easily 
be  cleaned  off.  The  ears,  handles  and  other  trimmings 
are,  as  far  as  is  practical,  welded  on,  as  riveted  joints  are 
difficult  to  enamel. 

Pickling  Process. — The  surfaces  of  the  completed 
steel  vessels  are  thoroughly  freed  from  carbonaceous 
matter  by  annealing  at  a  low  red-heat  and  are  then 
pickled  in  hot  dilute  acid,  thoroughly  rinsed  in  water, 
and  then  in  weak  alkali  solution.  After  a  quick  drying 
they  are  ready  to  be  enameled. 

The  Enamel. — In  the  making  of  an  enamel,  the  vari- 
ous raw-materials  are  loaded  from  their  respective  bins 

8 


into  small  cars  called  "dollies."  These  are  filled  to  a 
line  which  approximates  the  correct  weight,  then  they 
are  pulled  on  a  scale,  the  beam  of  which  is  hidden  from 
the  workman,  and  the  enamel-master  indicates  whether 
the  load  is  light  or  heavy,  and  the  workmen  correct  this 
by  shoveling  on  more  or  taking  some  off.  When  each  of 
the  "dollies"  is  corrected  so  that  the  required  amount  of 
material  for  a  mix  is  in  it,  all  are  dumped  on  a  large,  hard 
maple  floor,  the  coarser  material  on  the  bottom  and  the 
finer  on  the  top.  This  pile  is  thoroughly  mixed  by  shovel- 
ing, and  is  loaded  into  an  electric  elevator,  which  hoists 
it  to  its  bin.  There  is  a  bin  for  each  different  kind  of 
enamel,  and  a  traveling  bucket  which  holds  a  melt  (about 
1200  pounds)  carries  the  mix  to  the  tank  furnaces  where 
it  is  melted  into  a  liquid  glass. 

These  tank  furnaces  are  regenerative,  reverberatory 
furnaces  like  those  used  in  the  manufacture  of  glass,  and 
natural  gas  or  crude  oil  is  an  ideal  fuel  for  them.  How- 
ever, in  the  older  enameling  works,  coal  is  used  directly, 
and  in  the  later  ones  producer-gas  is  used  as  a  fuel.  The 
temperature  required  for  smelting  the  different  enamels 
varies  from  1000°  C.  for  a  glaze  to  1300°  C.  for  a  ground 
coat,  and,  in  most  enameling  works,  pyrometers  are  in- 
stalled to  assist  in  controlling  these  temperatures.  Each 
furnace  will  give  seven  or  eight  melts  in  twenty-four 
hours. 

After  the  enamel  is  melted  into  a  liquid  glass,  a  fire- 
clay plug  in  the  front  of  the  furnace  is  pulled  out  and 
the  glowing  liquid  stream  plunges  out  and  is  caught  in 
a  tank  of  cold  running  water.  The  reaction  is  terrific 
and  the  glass  mass  is  torn  and  shredded,  cracking  into 
small  pieces  like  popcorn,  each  of  which  is  a  myriad  of 
microscopic  seams  and  fissures.  This  "quenching,"  as 
the  process  is  called,  toughens  the  enamel  and  facilitates 
the  process  of  grinding  which  comes  next. 

The  water  is  drained  from  the  tanks,  leaving  the 
"enamel  frit."  This  is  shoveled  into  pans  (a  certain 
weight  to  a  pan)  and  is  ready  for  grinding. 

9 


In  the  mill  room,  the  enamel  frit  is  ground  in  large 
ball  mills  for  about  thirty  hours.  These  mills  are  cylin- 
drical, about  five  feet  long  and  six  feet  in  diameter,  and 
are  lined  with  porcelain  bricks.  The  frit  is  put  into  them 
with  fifty  per  cent,  of  water  and  several  per  cent,  of  white 
ball-clay.  For  the  white  cover-coat  enamels,  tin  oxide 
is  also  added.  The  mill  revolves  and  the  constant  impact 
of  the  flint  stones  against  the  glass  particles  grinds  them 
to  an  impalpable  powder,  which  mixes  with  the  water 
and  the  clay,  forming  a  mass  which  has  the  consistency 
of  rich  cream.  This  is  loaded  into  tanks,  where  it  is 
allowed  to  age  a  week  or  so. 

Application  of  the  Enamel. — From  the  mill  room  the 
enamel  is  taken  to  the  dipping  room,  where  it  is  put  into 
tanks  that  are  like  large  dish-pans.  These  are  sunk  into 
tables,  and  at  each  tank  a  slusher  works.  The  slusher 
takes  the  stamped-out  steel  vessel,  which  has  been 
thoroughly  cleaned,  and  plunges  it  into  the  enamel. 
When  taken  out,  the  wet  enamel  forms  a  thin  film  over 
the  entire  surface.  By  a  gentle  swinging  motion,  the 
excess  of  enamel  is  thrown  off,  and  the  vessel  is  placed 
bottom  down  on  three  metal  points  projecting  from  a 
board.  Three  or  four  vessels  are  put  on  a  board;  these 
are  placed  on  racks  and  when  the  vessels  are  thoroughly 
dry  they  are  carried  to  the  furnace  room. 

The  furnace  room  contains  a  long  bank  of  muffle- 
furnaces  and  in  these  the  ware  is  put  after  drying.  The 
temperature  in  these  furnaces  is  about  1000°  C.  and  here 
the  little  powdered  particles  of  enamel  are  fused  together 
in  a  solid  glass  coating  over  the  vessel,  the  process  re- 
quiring from  three  to  five  minutes. 

Each  coat  is  burned  separately.  For  instance,  we 
have  a  pudding  pan  that  is  to  be  a  three-coat  white  in- 
side, turquoise-blue  mottle  outside.  It  is  first  dipped  in 
the  ground  coat  enamel,  the  excess  is  shaken  off  and  the 
vessel  put  on  a  three-pointed  rack  and  dried.  After  dry- 
ing, the  enamel  stands  in  little  grains  all  over  the  surface 

10 


of  the  ware,  adhering  to  the  metal  on  account  of  the  raw 
clay  ground  with  it.  At  this  stage  every  care  must  be 
taken,  for  a  scraping,  even  of  the  finger  nail,  would  take 
off  some  of  the  powdered  particles  of  the  enamel.  This 
pan  is  then  put  into  the  muffle  of  the  furnace,  and  the 
heat  fuses  all  the  little  particles  together,  leaving  a  tight- 
holding  vitreous  coating  all  over  the  surface  of  the  vessel. 
This  fundamental  coating  is  nearly  black,  due  to  the 
oxides  of  cobalt  and  nickel  which  it  contains,  and  shines 
with  a  glass-like  luster. 

After  the  vessel  has  cooled  at  the  ordinary  tempera- 
ture of  the  room,  it  is  again  brought  to  the  slushing  room, 
and  here  is  covered  with  an  enamel — this  time  a  white. 
It  goes  through  the  same  process  as  before,  except  that 
a  black  bead  is  brushed  around  the  rim.  On  account  of 
the  dark  color  of  the  first  coat  showing  through,  this 
second  coat,  after  it  is  burned,  has  a  gray  appearance, 
and  is  called  the  "gray  coat"  or  "first  white."  The  vessel 
is  again  sent  to  the  slushing  room,  and  is  dipped  into  a 
white  enamel,  the  excess  shaken  off,  and  before  drying 
the  blue-green  enamel  is  sprayed  on  the  outside. 

This  spraying  process  was  at  one  time  done  by  dip- 
ping a  wire  brush  into  the  wet  blue-green  enamel  and 
the  slusher  shaking  it  over  the  surface  of  the  vessel,  caus- 
ing the  blue  enamel  to  fall  in  little  speckles  all  over  the 
white  enamel.  In  most  factories,  however,  spraying  ma- 
chines, which  work  on  the  principle  of  an  atomizer,  have 
been  installed.  A  tank  full  of  the  colored  enamel  stands 
over  the  table  and  the  enamel  is  forced  out  through  a 
nozzle  in  a  spray  by  compressed  air.  The  flowing  of  the 
enamel  is  controlled  by  the  foot  of  the  slusher  as  he  holds 
the  vessel  in  the  spray.  The  vessel  is  then  dried  and  the 
coating  is  fused  in  the  muffle-furnace,  the  result  being 
turquoise-blue  spots  on  a  white  background. 

The  finished  ware  is  assorted  into  three  lots:  firsts, 
seconds,  and  job  lots.  Some  of  the  seconds  and  job  lots 

11 


are  fit  for  redipping.  They  may  have  some  little  spots 
where  the  original  vessel  was  not  properly  cleaned  and 
where,  on  account  of  the  rust  or  dirt,  the  enamel  did  not 
adhere.  These  spots  are  filed  or  are  held  under  a  sand- 
blast until  the  exposed  surface  is  perfectly  clean,  and 
then  the  vessel  is  covered  with  another  coat  of  enamel. 

There  are  schemes  for  saving  money  in  all  manu- 
facturing plants,  and  in  the  enameling  business  a  large 
part  of  the  profit  comes  from  the  residues.  For  instance, 
every  bit  of  enamel  is  scraped  from  the  tanks  and  tables, 
all  sweepings  from  floors  are  saved,  and  all  the  waste 
water  from  the  various  departments  is  first  carried  into 
catch  basins,  and  every  few  days  these  are  cleaned  and 
the  residue,  which  has  settled  to  the  bottom,  is  taken  out. 
The  residues  from  all  these  sources  are  again  melted  with 
the  proper  amount  of  fluxing  material  and  coloring  mat- 
ter, and  this  dark-colored  enamel  is  used  for  coating  the 
cheaper  wares. 

A  German  White  Enamel. — In  order  to  give  an  idea 
of  the  composition  of  a  white  cover-coat  frit,  such  as  is 
used  on  cooking  utensils,  and  to  show  the  method  used 
by  ceramists  to  calculate  its  so-called  molecular  formula, 
the  following  enamel,  the  formula  of  which  is  taken  from 
the  19111  edition  of  the  "Taschenbuch  fur  Keramiker," 
is  used: 

Feldspar  38.6  per  cent.,  quartz  19.0  per  cent.,  borax 
15.4  per  cent.,  cryolite  11.7  per  cent.,  saltpeter  6.5  per 
cent.,  calcite  6.5  per  cent.,  fluorspar  1.3  per  cent,  and 
magnesium  carbonate  1.0  per  cent. 

Enamel  Materials. — All  the  materials  used  were 
practically  pure  except  the  feldspar,  which  was  a  peg- 
matite of  the  following  composition : 

1  Page  18.     Published  by  Keramische  Rundschau,  Berlin,  N.  W.,  21. 

12 


Per  cent. 

Silica    (SiO»)  70.66 

Alumina    AM)*  16.85 

Potassium  oxide    KaO  6.93 

Sodium   oxide    NaaO  4.61 

Lime   CaO  0.52 

Carbon  dioxide CO  0.41 

Moisture H*O  1.02 


This  figures  to  a  "molecular"  formula  of 


0.45  Na*Cn  f7.11SiO» 

0.39  KX)     [    AbO.    ^0.34H2Q 
0.06  CaO  J  L0.06CO» 

the  molecular  weight  of  which  would  be  602. 


The  other  materials  used  were : 

Equivalent 
Material  Formula  weight 

Quartz  SiO*    60 

Borax  Na*0  2B2O3  lOHsO     382 

Cryolite  2NasAlF6,  giving  3Na«O  AM>  6F»  ...      420 

Saltpeter  2K*0  N&s    202 

Calcite  CaO  CQ2 100 

Fluorspar  CaFs,  giving  CaO  F»    78 

Magnesium  carbonate  MgO  COa    84 

Feldspar  (Given  above)    602 

The  above  total  corresponds  to  the  following  molecu- 
lar formula  of  enamel : 


0.497  Na*O  ^  r2.513  SiO* 

0.186  K*O  0.262  B«O« 

0.278  CaO  0.299  AbO«   1  0.599  F» 
0.039  MgO  J 


RESEARCH  LABORATORY 

LISK  MANUFACTURING  Co.,  LTD., 

CANANDAIGUA,  N.  Y. 

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14 


THE  FUNCTION  OF  THE  VARIOUS  RAW  MATERIALS 
IN  A  SHEET  STEEL  ENAMEL* 

An  enamel,  such  as  is  used  on  cooking  utensils,  is  a 
glass  of  such  nature  that  it  will  adhere  to  steel  and  on 
account  of  this,  its  composition  is  more  complicated  than 
that  of  ordinary  glass.  The  materials  used  to  make  ordi- 
nary glass  are  sand,  limestone  and  soda  ash,  with  lead 
oxide  added  to  certain  types.  These  glasses,  however, 
will  not  adhere  to  iron  and  have  a  co-efficient  of  expan- 
sion entirely  different  from  that  of  sheet  steel,  and  also 
the  temperature  at  which  they  must  be  melted  would 
soften  the  steel  shape.  An  enamel,  then,  although  a  glass 
in  every  sense  of  the  word,  and  containing  the  elements 
introduced  by  these  glass  materials,  also  contains  others 
added  to  modify  the  physical  properties  and  to  suit  it  for 
the  purpose  intended. 

Quartz  and  Flint 

Sand  is  the  material  which  furnishes  silica  (SiO2)  to 
glass  and  it  is  sometimes  used  in  enamels.  However, 
enamels  must  melt  at  a  much  lower  temperature  than 
glass  and  thus  require  the  silica-furnishing  material  to 
be  very  finely  powdered  in  order  that  it  may  combine 
with  the  other  materials  at  this  lower  temperature.  As 
it  is  more  expensive  to  pulverize  sand  than  it  is  to  pul- 
verize quartz  or  flint,  one  of  these  minerals — each  hav- 
ing the  same  chemical  composition  as  sand — is  generally 
used. 

It  may  be  taken  as  a  general  rule  that  other  things 
remaining  constant,  the  higher  the  per  cent  of  silica  the 
higher  will  be  the  melting  point  of  the  enamel  and  the 


*Reprinted  from  original  communications,  Eighth   International  Congress  of 
Applied  Chemistry.     Vol.  XXV— Page  317. 

16  . 


greater  its  acid  resistance.  Silica  also  has  a  low  co-effi- 
cient of  expansion  and  increasing  it  in  an  enamel  lowers 
the  co-efficient  of  expansion  of  that  enamel.  Therefore, 
one  method  of  regulating  an  enamel  coating  is  to  increase 
the  silica  when  the  enamel  is  inclined  to  split  off  when 
cooling  after  muffle  burning.  This  remedy  is  indicated 
when  the  curve  of  the  enamel  chips,  showing  that  the 
enamel  contracts  less  rapidly  on  cooling  than  the  iron. 

Soda  Ash 

In  glass,  all  of  the  sodium  oxide  is  introduced  as  soda 
ash,  while  in  enamel,  this  material  is  only  used  when  it  is 
desirable  to  add  the  sodium  oxide  without  the  introduc- 
tion of  any  other  ingredient. 

Up  to  a  certain  point  the  addition  of  silica  to 
an  enamel  formula  may  lower  the  melting  point.  An 
exaggerated  example  is  that  Calcium  Oxide  (lime)  alone 
is  practically  infusible,  but  on  adding  silica,  a  fairly  easily 
fusible  glass  is  formed. 

Soda  Ash  is  commercially  pure  anhydrous  sodium 
carbonate  (Na2CO3)  and,  therefore,  besides  adding  the 
sodium  oxide  to  the  finished  enamel,  gives  off  carbon-di- 
oxide gas  during  smelting  and  the  melted  mass  is  then 
quite  thoroughly  stirred  by  the  evolution  of  this  gas  and 
many  impurities  are  carried  off. 

The  function  of  the  sodium  oxide  is  to  combine  with 
the  other  materials  (especially  the  silica)  and  form  a 
vitreous  product.  The  larger  the  proportion  of  sodium 
oxide  (in  comparison  with  the  amount  of  silica  present) 
the  lower  will  be  the  melting  point  of  the  product  and  the 
less  resistant  to  acids  it  will  be.  At  the  same  time,  how- 
ever, an  increase  of  the  sodium  oxide  tends  to  make  the 
product  more  flexible  and  less  brittle. 

Many  enamels  do  not  include  soda  ash  in  their  batch 
mix  formulas  as  sufficient  sodium  oxide  is  furnished  by 
the  feldspar,  cryolite  and  borax. 

16 


Fluorspar  and  Calcite 

Fluorspar  and  Calcite  are  the  minerals  which  are 
used  to  supply  the  lime  (CaO)  to  enamels.  In  glass, 
limestone  furnishes  this  important  ingredient,  but  on  ac- 
count of  the  impurities,  always  present  in  this  mineral, 
it  cannot  be  used  in  the  more  carefully  compounded  enam- 
els. Both  Fluorspar  and  Calcite  have  their  advantages 
and  disadvantages  and,  as  their  cost  is  about  the  same, 
a  careful  consideration  of  these  is  necessary  before  one 
can  decide  which  is  the  better  to  use  in  an  enamel.  Ameri- 
can practice  is  inclined  to  favor  the  use  of  Fluorspar. 

Fluorspar 

The  calcium  present  in  Fluorspar  seems  to  combine 
more  easily  with  the  other  ingredients  of  the  enamel 
batch  than  does  the  calcium  oxide  of  calcite.  This  is 
evident  from  the  fact  that  Fluorspar  enamels  melt  at  a 
lower  temperature  and  become  homogeneous  in  a  shorter 
time  than  calcite  enamels.  In  enamels,  which  derive  some 
of  their  opacity  from  cryolite,  this  is  of  particular  advan- 
tage, for  it  is  a  well  known  fact  that  the  longer  a  cryolite 
enamel  is  smelted,  the  less  opaque  it  becomes. 

The  disadvantages  pertinent  to  the  use  of  fluorspar 
instead  of  calcite  in  an  enamel  formula  are  due  to  two 
things;  this  mineral  contains  fluorine  and  is  a  powerful 
reducing  agent  at  the  temperature  attained  in  the  smelter. 
The  fluorine  is  set  free  during  the  smelting  and,  although 
the  virtues  of  fluorspar  are  very  likely  due  to  the  ener- 
getic action  of  this  element,  it  is  also  active  in  corroding 
the  furnace  linings  and  the  life  of  the  smelter  is  short- 
ened. 

The  reducing  action  of  this  mineral  makes  it  very 
necessary  to  carefully  regulate  the  smelter  so  that  the 
atmosphere  is  always  oxidizing  and  where  a  large  amount 
is  used  the  percentage  of  nitrate  in  the  batch  mix  must 
be  increased. 

17 


Calcite 

Calcite  in  enamels  does  not  act  as  a  reducing  agent 
nor  does  the  gas  given  off  by  it  (CO2)  attack  the  furnace 
linings.  Therefore,  the  life  of  the  smelter  is  longer  and 
there  is  no  necessity  for  adding  more  nitrate  nor  of  so 
carefully  controlling  the  atmosphere  of  the  smelter. 

The  disadvantages  common  to  a  calcite  enamel  are 
due  to  its  requiring  a  higher  temperature  and  a  longer 
time  to  combine  with  the  other  ingredients  of  the  batch. 
With  cryolite  enamels,  this  longer  smelting  is  certain  to 
cause  them  to  lose  some  of  their  opacity.  . 

Defects  Caused  by  Fluorspar  and  Calcite 

Unless  sufficiently  smelted  and  thoroughly  oxidized, 
fluorspar  enamels  are  not  stable  and,  on  standing,  lose 
their  gloss,  while  calcite  enamels,  unless  smelted  entirely 
homogeneous  and  free  from  carbonate,  are  inclined  to 
chip  and  scale  and  to  form  hubbies  and  blowholes  where 
the  enamel  is  applied  thickest.  - 

Calcium  Oxide  (CaO) 

The  calcium  oxide  introduced  by  either  of  these  ma- 
terials will  replace  sodium  oxide  in  an  enamel  formula 
and,  while  not  affecting  the  melting  point  to  any  great 
extent,  makes  the  enamel  much  harder,  more  acid  resist- 
ant, more  glossy  and  more  opaque.  Calcium  oxide  in- 
creases the  brittleness  of  an  enamel,  however,  but  at  the 
same  time  it  allows  the  addition  of  more  boric  anhydrid 
and  this  ingredient  counteracts  this  effect. 

Feldspar 

Feldspar  is  generally  included  in  the  batch  mix  of 
any  enamel.  The  new  element  introduced  by  this  ma- 
terial is  aluminum  in  the  form  of  alumina  (A12O3).  It 
also  adds  sodium  oxide  (Na2O)  or  potassium  oxide  (K2O) 
or  both  and  at  a  much  cheaper  price  per  pound  than 
they  can  be  bought  in  any  other  form. 

18 


The  other  ingredient  introduced  by  feldspar  is  silica 
(SiO2)  and  it  is  likely  that  its  introduction  thus  has  the 
advantage  over  its  introduction  as  quartz  or  flint,  in  that, 
in  feldspar,  nature  has  already  combined  the  alumina  and 
the  silica.  An  enamel,  therefore,  getting  its  silica  from 
feldspar  requires  less  heat  in  smelting  than  one  getting 
the  silica  otherwise. 

The  alumina  added  by  the  feldspar  makes  the  glass 
softer  and  also  less  resistant  to  acids,  but  when  other 
suitable  ingredients  are  present,  causes  the  enamel  to  be- 
come translucent.  It  also  lessens  the  tendency  of  the 
enamel  to  chip  but  makes  it  more  liable  to  craze.  It  com- 
bines directly  with  the  other  ingredients  forming  a  homo- 
geneous product  and,  therefore,  does  not  aid  in  improving 
the  stretching  qualities  of  the  product  as  does  the  alumina 
added  as  clay,  which  material  will  be  taken  up  later. 

Borax  and  Boric  Acid 

One  of  the  most  characteristic  ingredients  of  an  en- 
amel is  boric  anhydrid  (B2O3)  and  this  is  furnished  to 
the  batch  mix  by  borax  or  boric  acid. 

Borax  is  generally  used  for  this  purpose,  as  it  is 
much  cheaper  and  the  only  enamel  in  which  its  use  is 
prohibited  are  those  whose  full  quota  of  sodium  oxide  is 
furnished  by  the  feldspar  and  cryolite.  Borax  contains 
16%  of  sodium  oxide,  so  in  such  enamels,  boric  acid 
(B2O3.3H2O)  would  be  used. 

Boric  anhydrid  (B2O3)  makes  the  enamel  more  elas- 
tic, less  brittle  and  changes  the  co-efficient  of  expansion  in 
such  a  way  that  the  glass  produced  may  be  used  on  steel. 
It  is  like  the  silica  in  many  ways,  increasing  the  acid  re- 
sistance and  allowing  more  alkalies  and  metal  and  earth 
oxides  to  be  used  in  the  mix  and  like  silica  causes  the 
enamel  to  chip  when  present  in  excess. 

Unlike  silica,  however,  it  increases  the  viscosity  of  the 
smelted  enamel  and  lengthens  the  period  between  the 
temperature  at  which  the  enamel  will  melt  to  form  a 

19 


homogeneous  vitreous  coating  and  the  temperature  at 
which  it  will  "burn  off,"  thus  making  the  enamel  less 
liable  to  be  spoiled  by  poor  shop  practice. 

This  property  of  viscosity,  which  the  boric  anhydrid 
increases,  causes  the  enamel  to  remain  thick  and  gummy 
on  the  black  shape,  while  being  heated  in  the  muffle,  in- 
stead of  getting  thin  and  running  off  as  would  ordinary 

glass. 

Clay 

Clay  is  always  used  in  the  mill  mix  of  an  enamel  that 
is  to  be  slushed  on  wet  and  is  sometimes  included  in  the 
ingredients  that  go  into  the  smelter.  In  the  latter  case, 
it  is  used  to  introduce  alumina  and  silica,  as  does  feldspar, 
but  without  introducing  any  alkalies.  Clay  is  quite  in- 
fusible and  very  finely  divided,  thus  adding  opacity  to  the 
enamel.  When  added  at  the  mill,  it  gives  besides  the 
qualities  already  mentioned  plasticity  to  the  wet  enamel 
and  holds  up  the  glass  particles  during  slushing.  It  also 
causes  the  powdered  glass  particles  to  adhere  to  the  steel 
shape  during  the  drying  before  muffle  burning. 

Whether  added  at  the  mill  or  in  the  smelter,  clay 
adds  to  the  stretching  qualities  of  the  finished  enamel 
coating.  This  is  accounted  for  by  the  infusibility  of  the 
clay,  with  property  keeps  it  from  entering  into  complete 
combination  with  the  other  materials.  Instead,  it  holds 
the  glass  masses  (with  which  each  particle  of  clay  is  sur- 
rounded) apart  during  the  contraction  of  the  steel  and 
allows  them  to  pull  away  from  it  without  chipping  dur- 
ing expansion.  Under  the  microscope,  enamels  with  a 
high  clay  content  are  very  porous — the  higher  the  clay 
the  more  porous — and,  therefore,  clay  in  an  enamel  al- 
ways lessens  the  gloss.  This  is  the  prime  factor  in  limit- 
ing the  amount  of  clay  that  can  be  used  in  an  enamel. 

Stellmittle 

The  plasticity  of  clays  in  water  can  be  greatly  in- 
creased by  adding  to  the  water  very  small  quantities  of 
acids,  bases  or  salts  which  dissociate  in  the  water.  These 

20 


cause  the  clay  to  assume  a  colloidal  form  quite  jelly-like 
in  nature  and  thus  make  the  enamel  batch  in  which  they 
are  present  much  thicker  without  removing  any  of  the 
water. 

These  are  called  "Stellmittle"  or  fixation  materials 
by  the  German  enamelers.  Any  acid  will  answer,  but, 
as  the  effect  on  the  finished  product  is  deleterious,  these 
are  seldom  used.  Borax  (a  saturated  solution  in  hot 
water)  or  a  mixture  of  this  with  a  saturated  solution  of 
sodium  carbonate  is  generally  used  in  ground  coat  enam- 
els and  may  be  used  in  small  quantities  in  white  enamels. 
Magnesium  Sulfate  has  much  favor  with  most  enamelers 
and  its  principal  virtue  is  that  less  of  it  is  required  than 
of  any  of  the  others.  Magnesium  sulfate  cannot  be  used 
in  the  ground  coat,  as  it  will  cause  the  iron  to  rust. 

Magnesium  Oxide  and  Carbonate  are  used  in  the 
mill  mix  and  are  good  for  this  purpose,  as  also  is  ammo- 
nium chloride,  ammonium  carbonate  and  ammonium  ace- 
tate. Some  enamelers  also  use  the  sulfate  of  sodium  but 
any  of  the  sulf  ates  will  impair  the  gloss  of  the  product. 

Oxide  of  Tin 

Tin  oxide  is  one  of  the  most  important  a,nd,  at  the 
same  time,  most  expensive  of  the  enameling  materials. 
Indeed  a  French  writer  defines  an  enamel  as  "an  opaque 
glaze  containing  tin  oxide." 

Added  to  the  smelting  batch,  up  to  about  3%  of  the 
stannic  oxide— the  commercial  oxide  of  tin — is  reduced 
to  stanous  oxide,  which  forms  a  transparent  compound 
with  the  silica.  All  over  3%,  and  practically  all  added 
at  the  mill,  remains  in  suspension  in  the  enamel,  and, 
keeping  its  intense  white  color,  makes  the  enamel  opaque. 

The  writer  has  used  as  high  as  30%  of  this  material 
in  an  excellent,  though  costly,  enamel,  but  the  amount 
used  in  white  enamels  for  cooking  utensils  seldom  runs 
below  5%  or  above  15%  in  the  finished  product. 

21 


All  efforts  to  entirely  replace  this  material  with  a 
cheaper  one  have  led  to  the  conclusion  that  some  oxide 
of  tin  is  absolutely  necessary  in  a  white  enamel.  Other 
materials  can  replace  part  of  it,  but  the  question  as  to 
whether  there  is  any  actual  saving  in  so  doing  is  a  matter 
of  dispute. 

The  higher  the  percentage  of  tin  oxide  in  an  enamel 
the  thinner  it  may  be  applied  and  attain  a  given  standard 
of  whiteness.  This  thin  application  reduces  the  produc- 
tion cost  in  two  ways,  viz.,  less  enamel  is  required  and  the 
number  of  seconds,  caused  by  the  scaling  off  of  the  too 
thick  coatings,  will  be  greatly  reduced.  But  of  still  more 
importance  is  the  fact  that  the  thin  application  of  the 
enamel  adds  greatly  to  the  durability  of  the  ware  under 
punishment  both  by  impact  and  by  sudden  changes  of 
temperature,  thus  adding  to  the  reputation  of  the  manu- 
facturer. Then  too,  the  opacity  produced  by  this  mate- 
rial is  practically  "fool  proof."  The  tin  oxide  substitutes 
must  be  handled  with  the  greatest  of  care  during  every 
operation  and  the  slightest  variation  of  method  of  proce- 
dure is  likely  to  spoil  the  enamel. 

Cryolite 

The  only  material  which  produces  opacity  besides 
the  tin  oxide  and  which  has  stood  the  test  of  time  is  cryo- 
lite. This  material  must  be  added  in  the  smelter  and  al- 
though it  adds  no  new  elements  those  added  are  so  geo- 
logically combined  that  at  a  certain  temperature  they 
make  the  enamel  frit  quite  translucent  and  even  opaque 
when  thickly  applied.  The  amount  of  this  material  which 
can  be  used  in  a  given  enamel  is  limited  by  the  large 
amount  of  sodium  oxide  which  it  introduces.  Cryolite 
is  a  double  fluoride  of  aluminum  and  sodium  and  in  the 
enamel  about  20%  of  its  mass  escapes  as  fluorine  gas  and 
is  replaced  by  oxygen.  Thus  it  is  very  necessary  to  keep 
the  atmosphere  of  the  smelter  oxidizing,  and  this  is  best 
done  by  having  sufficient  nitrate  present  in  the  enamel 
batch.  The  opacity  produced  by  cryolite  is  quite  elusive 

22 


and  the  greatest  care  must  be  taken  to  have  the  tempera- 
ture, both  of  the  smelter  and  the  muffle  furnace,  right 
and  the  length  of  time  for  smelting  and  burning  correct. 

Oxide  of  Antimony 

Antimony  Oxide  is  another  substitute  for  tin  oxide 
and  like  cryolite  this  is  added  in  the  smelter.  Antimony- 
containing  enamels  are  quite  opaque,  if  applied  in  thick 
layers;  thin  coats  of  such  enamels,  however,  are  quite 
transparent  and  it  is  doubtful  whether  or  not  antimony 
has  any  great  coloring  effect  on  a  properly  applied 
enamel.  Antimony  oxide  is  in  itself  quite  poisonous  and 
when  used  in  quantities  large  enough  to  give  the  desired 
opacity,  there  is  a  danger  that  some  of  it  may  be  made 
soluble  in  the  cooking  acids  and  thus  be  detrimental  to 
the  health  of  the  consumer.  In  practice  most  antimony 
enamels  contain  less  than  5%  of  this  material. 

Both  antimony  and  tin  oxide  and,  in  fact,  all  metallic 
oxides  add  lustre  to  the  enamel  coating,  for  they  increase 
the  density  and  it  has  been  shown  that  the  gloss  of  a  glass 
or  enamel  increases  directly  with  the  density. 

Zinc  Oxide 

The  oxide  of  zinc  is  the  only  metallic  oxide,  except 
that  of  tin,  which  can  be  safely  added  to  a  white  enamel 
for  the  purpose  of  increasing  its  luster,  and  even  it  will 
lower  the  resistance  to  corrosion  by  acids  of  such  an  en- 
amel very  markedly. 

Used  in  large  quantities  and  in  very  soft  enamels  it 
produces  some  opacity.  Its  main  use,  however,  is  as  a 
substitute  for  the  objectionable  lead  oxide  in  formulas 
for  colored  enamels.  Like  lead,  it  has  the  property  of 
making  such  colors  more  brilliant. 

Saltpeter  and  Chili  Saltpeter 

Potassium  nitrate  (saltpeter)  or  sodium  nitrate 
(Chili  Saltpeter)  is  used  in  enamels,  which  require  ox- 
idizing agents  in  the  smelter. 

23 


Oxidizing  agents  are  necessary  in  enamel  formulas 
which  contain  fluorspar  or  cryolite  to  replace  the  fluorine 
given  off  in  the  smelter  and  also  in  white  enamels  con- 
taining iron  as  an  impurity.  In  the  latter  case,  they 
change  all  of  the  iron  to  the  higher  oxide  which  has  a  less 
intense  coloring  action  on  the  enamel. 

Sodium  nitrate  is  much  cheaper  than  potassium  ni- 
trate but  must  be  stored  in  air  tight  containers  as  it  is 
very  deliquescent.  The  impracticability  of  storing  the 
material  has  forced  manufacturers  to  use  the  more  ex- 
pensive nitrate  or  to  employ  a  chemist  to  make  daily  de- 
terminations of  its  moisture  content.  Then  too,  experi- 
ment has  shown  that  the  presence  of  potash  in  an  enamel 
already  containing  soda  tends  to  increase  the  gloss  and 
to  lower  the  melting  point  without  affecting  the  other 
properties.  This  would  be  a  reason  for  using  nitrate  of 
potash  instead  of  nitrate  of  soda  in  an  enamel,  in  which 
potash  is  not  supplied  by  some  other  material,  for  potas- 
sium oxide  remains  from  the  saltpeter,  while  sodium  oxide 
remains  from  the  Chili  saltpeter. 

Manganese  Di-Oxide 

Manganese  di-oxide  (MnO2)  is  a  strong  oxidizing 
agent  and  its  use  in  enamels  is  primarily  due  to  this  fact. 
Used  in  an  enamel  batch,  it  disintegrates  during  smelting 
into  manganous  oxide  (MnO)  and  oxygen  gas  and  the 
latter,  besides  stirring  the  molten  enamel,  changes  some 
of  the  ingredients  to  their  highest  possible  oxides. 

This  action  is  especially  desirable  in  ground  coats 
which  must  stand  a  hot  fire  in  the  muffle,  as  it  renders 
over-burning  during  this  operation  less  probable. 

Manganese  compounds  cannot  be  used  in  white  en- 
amels in  more  than  minute  quantities  as  it  colors  the  glaze 
an  amethyst  purple.  Its  second  use  in  enamels  is  due 
to  this  coloring  action  and  it  is  used  in  many  colored 
enamels. 

24 


Oxide  of  Cobalt 

Oxide  of  Cobalt  (CO3O4)  is  added  to  enamels  either 
to  give  them  a  blue  color  or  to  make  them  adhere  directly 
to  the  steel.  For  the  second  reason,  all  successful  ground 
coats  contain  oxide  of  cobalt.  An  enamel  may  be  so  com- 
pounded that  its  co-efficient  of  expansion  will  be  exactly 
that  of  the  sheet  steel  upon  which  it  is  to  be  used,  and, 
yet  without  the  addition  of  oxide  of  cobalt,  according 
to  the  writer's  experience,  it  cannot  be  made  to  adhere 
to  the  steel  as  well  as  with  this  addition.  There  are 
many  theories  as  to  the  exact  function  of  cobalt  in  a 
ground  coat  enamel  and  the  popular  one  at  present,  is  that 
silicate  of  cobalt  in  the  enamel  frit  is  reduced  during 
muffle  burning  to  a  lower  silicate  and  perhaps  to  metallic 
cobalt.  The  oxygen,  which  is  given  off  in  either  case  then 
unites  with  the  iron  of  the  black  shape  and  is  taken  into 
the  enamel  as  ferrous  silicate  and,  if  metallic  cobalt  is 
left,  this  unites  with  the  iron  of  the  black  shape,  forming 
a  widely  distributed  porous  alloy.  At  any  rate,  there  is 
an  interaction  between  the  cobalt  of  the  enamel  and  the 
iron  of  the  black  shape  which  binds  the  enamel  to  the 
steel.  Whether  this  is  the  correct  explanation  of  the  ac- 
tion, we  do  not  know,  but  it  is  certain  from  practical  ex- 
perience that  the  cobalt-containing  ground  coat  enamels 
are  more  easily  burned  correctly  by  the  men  in  charge 
of  the  muffle  furnaces.  This  is  explained  by  the  fact  that 
there  is  a  definite,  though  delicate,  color  change  from 
blue  to  green  in  cobalt-containing  ground  coat  enamel? 
at  just  the  point  at  which  the  enamel  so  fired  will  adhere 
most  firmly  to  the  steel  coat.  Such  an  enamel,  when  cor- 
rectly burned,  will  have  a  very  characteristic  greenish 
tinge;  when  under-burned  a  blue  color,  and,  when  over- 
burned,  a  brownish  black  color. 


25 


RESISTANCE  OF  SHEET  STEEL  ENAMELS  TO 
SOLUTION  BY  ACETIC  ACIDS  OF 
VARIOUS  STRENGTHS* 

Certain  enameled  wares  have  been  advertised  as 
capable  of  withstanding  80  per  cent,  or  90  per  cent,  acetic 
acid  solutions,  and  although  this  was  found  to  be  a  true 
statement  still  it  was  misleading,  for  these  very  wares 
were  unable  to  resist  the  action  of  ordinary  vinegar  which 
contained  but  5  per  cent,  acetic  acid.  This  phenomenon 
is  explained  by  the  chemist  as  being  due  to  the  fact  that 
a  5  per  cent,  solution  of  acetic  acid  is  very  much  more  dis- 
sociated than  one  of  80  or  90  per  cent,  and  therefore  its 
dissolving  action  (which  is  directly  proportional  to  its  dis- 
sociation) is  much  the  greater. 

To  show  the  action  of  various  mixtures  of  this  com- 
mon cooking  acid  and  water,  the  two  series  of  tests  were 
made  upon  enamels  typical  of  some  of  the  cheap  wares 
on  the  market. 

The  First  Series  of  experiments  was  made  upon  a 
gray  enamel,  mottled  with  dark  brown.  As  the  dark 
enamel  was  made  up  from  residues,  and  as  the  propor- 
tions of  the  two  enamels  on  the  dishes  is  uncertain,  the 
exact  molecular  formula  of  the  finished  enamel  coating 
cannot  be  given,  but  the  formulas  as  calculated  from  the 
batch  mix  of  the  gray  enamel  and  the  analysis  of  the  dark 
enamel  frit  (before  milling)  is  given  below. 

THE  ENAMELS 

Soft  Gray  Enamel1 

0.667  Na*O        ]  f  1.065  SiO* 

0.108  KX) 

0.083  CaO         \-    0.272  AfcOs   4  0.402 
0.057  MgO 

0.085  ZnO        J  1 0.532 

Milled  with  1%  clay 


*Reprinted  from  Transactions  of  American  Ceramic  Society.    Vol.  XIII,  page  494. 

1  So  called,  as  it  is  translucent  instead  of  opaque  and  when  milled  without  tin 
oxide — as  was  the  case  above — the  dark  ground  coat  shows  through  giving  a  gray 
effect. 

26 


0.430 
0.083  KX) 
0.200  CaO 
0.045  MgO 
0.056  CuO 
0.010  CoO 
0.176  MnO 


Soft  Dark  Enamel  for  Spray 

rl.700  SiCh 


0.114  AK)a 


0.430 


10.178 


Milled  with  1%  clay 


The  Test 

Nineteen  miniature  wash-basins  about  8.5  centi- 
meters in  diameter  and  2  centimeters  in  depth  were 
slushed  and  burned  in  a  dark  colored  ground  coat,  and 
then  dipped  into  the  gray  enamel  slush  and  when  the 
excess  was  shaken  off  a  light  spray  of  the  dark-colored  en- 
amel was  flipped  in  with  a  brush.  After  drying  they  were 
burned  at  about  Seger  cone  09  in  a  muffle  furnace.  They 
were  cooled  in  a  desiccator  and  weighed  accurately  to 
one-tenth  of  a  milligram  (0.0001  gram).  Into  one  of  them 
was  accurately  measured  (from  two  burettes  graduated 
to  1/10  of  a  cubic  centimeter)  0.25  cubic  centimeter  acetic 
acid1  and  24.75  cubic  centimeters  distilled  water,  making 
a  1  per  cent,  solution  by  volume.  Into  a  second  dish  was 
measured  (as  before)  sufficient  acid  and  water  to  make 
a  2  per  cent,  solution.  Into  a  third  a  3  per  cent,  and  so  on 
as  given  in  the  table  following.  These  basins  were  then 
placed  upon  a  gas  hot-plate  and  evaporated  to  dryness 
without  allowing  them  to  boil  vigorously. 

When  baked  dry  (fifteen  minutes  after  apparent  dry- 
ness)  the  dissolved  residue  was  washed  out  at  the  tap,  the 
dishes  were  scrubbed  with  a  finger  covered  with  a  rubber 
finger-stall,  rinsed  thoroughly  with  distilled  water,  placed 
upon  the  hot-plate  again  until  dry,  cooled  in  a  desiccator 
and  again  weighed.  The  loss  in  weight,  which  is  equal 
to  the  amount  of  enamel  dissolved  in  each  case,  is  given 
below  in  milligrams. 


1  This  acetic  acid  was  the  ordinary  c.  p. 
tained  98.99%  acid  by  weight. 

27 


(1.05  sp.  gr.)   and  by  analysis  con- 


The   Results 


Per  cent 
acid 
1  

Enamel 
dissolved 
Mg 
4.8 

2 

6.9 

3  

....      10.1 

4 

12  1 

5 

14  9 

7  

16.9 

9  

18.5 

15 

21  3 

17  

22  0 

20.  . 

22.4 

Per  cent 
acid 
25      . 

Enamel 
dissolved 
Mg 
17  9 

30  

18.9 

40  

13.0 

50  

8.9 

60  

5.0 

70  

3.1 

80  

1.6 

90  

0.3 

100.  . 

0.0 

The  Second  Series  was  undertaken  upon  an  enamel, 
the  definite  molecular  formula  of  which  can  not  be  given. 


The    Enamel    used    was    "soft    gray    enamel,' 
molecular  formula  of  which  is  given  above. 


the 


The  Test  used  was  the  same  as  with  the  first  series 
except  that  the  miniature  wash-basins  were  slushed  and 
burned  in  three  coats,  viz.,  a  dark  ground,  a  good  opaque 
white,  and  the  "soft  gray  enamel"  given  above  which 
was  the  top  coat.  These  dishes  are  on  exhibition  and 
the  results  are  given  in  the  following  table. 


Per  cent 
acetic  acid 
1 

The 

Enamel 
dissolved 
Mg 

3  4 

Results 

Per  cent 
acetic  acid 
21        

Enamel 
dissolved 
Mg 
....      14.0 

2 

5  7 

23  

12.0 

3. 

7.0 

25  

9.9 

4  

9.3 

30  

11.3 

5  

11.5 

40  

10.3 

7 

15  1 

50 

7.9 

9 

15  9 

60  

4.6 

11  

16.3 

70  

2.8 

13 

16  6 

80 

1.4 

15  .  .  '. 

16  7 

90  

0.2 

17  

.    .        16.3 

100  

0.0 

19.. 

14.7 

28 


The  Enamel  Solubility  Curves 

The  accompanying  sketch  shows  graphically  the  re- 
sults of  these  two  series  of  experiments.  The  various 
percentages  of  acetic  acid  solutions  are  laid  off  horizon- 
tally and  the  lengths  of  the  vertical  lines  are  proportional 
to  the  amount  of  enamel  dissolved  by  the  corresponding 
acid,  one  centimeter  length  of  vertical  line  being  equal 
to  one  milligram  of  dissolved  enamel.  The  results  of  the 
first  series,  i.  e.,  the  one  using  the  mottled  enamel,  are 
marked  "X,"  while  those  of  the  second  series,  i.  e.,  of 
the  solid-colored  enamel  are  marked  "o." 

N.  B.  The  dip  of  the  two  curves  from  21  per  cent,  to 
30  per  cent,  acid  is  unexplained.  Several  independent 
trials  at  those  points  tended  towards  proving  that  this  dip 
is  not  due  to  experimental  error. 

Discussion 

MR.  STALEY:  This  paper  is  interesting  and  in- 
structive. As  a  practical  method  of  testing  the  relative 
solubility  of  enamels  in  acid  solutions,  the  method  de- 
scribed has  the  commendable  feature  of  being  easily  and 
rapidly  performed.  In  point  of  accuracy,  it  is  capable  of 
being  materially  improved. 

The  shape  of  the  solubility  curve  derived  is  very  in- 
teresting. That  the  solubility  should  decrease  as  the  acid 
becomes  very  concentrated  is  in  accord  with  common  ex- 
perience.1 But  why  should  the  solubility  be  greatest  at 
15  to  20  per  cent,  acid?  Dissociation  can  hardly  be  at  a 
maximum  at  this  high  concentration.  Nor  are  we  willing 
to  grant  that  the  solvent  action  of  acetic  acid  is  directly 
proportional  to  its  dissociation.  If  we  leave  out  of  con- 
sideration the  possibility  that  the  acid  solution  may  act 
toward  the  enamel  simply  as  a  solvent,  dissolving  it  as 
water  dissolves  sugar,  and  treat  the  phenomena  as  a  case 
of  chemical  attack  by  an  acid,  we  must  keep  in  mind  the 
following  considerations : 

1  Foerster,  "Action  of  Acids  on  Glass,"  Zeitschrf .  Instraum.,  XIII,  457. 

29 


30 


1.  In  dilute  acid  solutions,  the  acid  is  more  disso- 
ciated than  in  concentrated  solutions.  This  of  itself  means 
simply  that  we  will  have  more  action  in  a  given  time  per 
unit  of  acid  and  does  not  mean  that  the  more  highly  ion- 
ized acid  is  capable  of  dissolving  more  enamel  if  the  reac- 
tions are  allowed  to  come  to  equilibrium. 

2.  Dilute  acid  solutions  contain  fewer  units  of  acid. 

3.  Very  highly  concentrated   acid   solutions  have 
little  action. 

4.  The  concentration  of  the  acid  solutions  varied 
continuously  as  they  were  boiled,  becoming  more  and 
more  concentrated  as  the  boiling  progressed.    Therefore, 
the  more  dilute  the  acid  the  longer  the  time  in  which  ac- 
tive concentrations  would  be  operating.     It  also  follows 
from  this  that  the  slower  the  rate  at  which  the  acid  is 
concentrated,  the  greater  will  be  its  solvent  action. 

In  accordance  with  these  conflicting  tendencies,  we 
find  the  acid  solutions  of  maximum  solvent  action  are 
those  of  medium  concentrations. 

Acetic  acid  is  one  of  the  few  organic  acids  that  does 
not  form  a  mixture  of  constant  boiling  point  with  water. 
The  pure  acid  boils  at  118°  C.  and  in  water  solutions  the 
water  will  start  to  come  off  at  100°C.,  and  will  come  off 
the  more  rapidly  the  higher  the  temperature.  So,  if  we 
should  start  with  a  given  volume  of  what  would  be  in  this 
method  approximately  a  5  per  cent,  solution  by  volume 
of  acetic  acid  and  place  it  on  a  hot  gas  plate,  we  would 
soon  have  a  smaller  volume  of  10  per  cent.,  then  20  per 
cent,  and  so  on  up  to  a  very  small  volume  of  100  per  cent, 
acid.  The  resulting  solvent  action  would  probably  vary 
materially  from  what  would  be  obtained  by  a  treatment 
for  a  given  time  with  an  acetic  acid  solution  of  5  per  cent, 
strength.  The  latter  results  which  would  truly  corre- 
spond to  the  title  of  the  paper  under  discussion  could  be 
obtained  by  the  use  of  a  return  condenser. 

31 


Nc.  of  sample 
1     

Per  cent  of 
acetic  acid 
15 

Time  for 
evaporation 
in  minutes 
65 

2 

15 

65 

3 

15 

155 

4 

15 

155 

In  order  to  determine  the  effect  of  the  rate  of  evapo- 
ration on  the  solvent  action  of  an  acid  solution  of  given 
strength,  the  following  tests  were  made  by  the  writer. 
Four  pans  coated  with  the  same  enamel  were  treated 
according  to  this  method,  the  only  variation  in  their  treat- 
ment being  that  two  pans  were  placed  on  a  hot  portion 
and  two  on  a  cooler  portion  of  the  same  gas  hot-plate. 
Violent  boiling  did  not  occur  in  either  case. 

The  results  are  tabulated  below: 

Enamel 
dissolved 
Mg 
20.9 
19.1 
37.8 
39.0 

It  would  seem  that  in  a  test  of  this  kind  a  constant 
temperature  bath  should  be  employed. 

MR.  LANDRUM :  I  agree  with  Mr.  Staley  that  my 
title  is  rather  misleading  and  might  infer  that  this  paper 
is  intended  as  a  research  in  pure  chemistry  instead  of 
being  merely  a  statement  of  the  results  of  a  series  of 
practical  tests  made  to  demonstrate  in  a  quick  and  con- 
vincing way  the  fact  that  an  enameled  ware  may  with- 
stand the  action  of  boiling  90  per  cent,  acid  and  still  be 
attacked  by  acid  solutions  even  as  dilute  as  those  used 
in  cooking. 

In  these  tests  the  conditions  were  very  carefully  kept 
as  uniform  as  possible,  and  I  might  add  that  acetic  acid 
and  the  method  of  boiling  to  dryness  were  used  simply 
because  I  was  trying  to  duplicate  the  method  used  on  the 
ware  advertised  as  "90  per  cent,  acid  proof."  I  also 
would  like  to  state  that  in  these  series  of  tests  all  the 
dishes  in  each  series  were  put  on  the  hot  plate  at  the  same 
time  and  that  this  plate  was  of  the  type  given  an  even 
temperature  to  all  parts  of  the  plate  (see  E.  H.  Sargent's 
catalog  for  cut  of  plate  No.  2406).  While,  as  stated,  the 

32 


solutions  were  not  allowed  to  boil  vigorously,  they  were 
allowed  to  boil  down  as  rapidly  as  possible  without  spat- 
tering. From  eighteen  to  twenty  minutes  were  required 
to  boil  to  dryness. 

I  certainly  do  not  advocate  this  as  a  method  for  test- 
ing the  acid-resistance  of  enameled  wares  and  agree  with 
Mr.  Staley  that  for  a  research  as  that  seeminly  indi- 
cated by  my  title,  a  constant-temperature  bath  and  a  re- 
flux condenser  should  be  used.  However,  for  purposes 
of  duplicating  the  treatment  received  by  an  enameled 
dish  in  actual  use  this  method  of  showing  the  action  of 
various  acetic  acid  solutions  might  have  some  points  in 
its  favor  over  the  more  accurate  one  suggested. 


33 


A  COMPARISON  OF  TEN  WHITE  ENAMELS  FOR 
SHEET  STEEL* 

This  paper  is  the  record  of  the  manufacturing  and 
description  of  the  physical  properties  of  ten  white  enam- 
els. It  is  given  not  with  the  idea  of  presenting  to  ceramic 
literature  a  set  of  commercial  formulas,  but  to  illustrate 
a  method  for  testing,  arranging  the  data,  and  arriving 
at  the  comparative  values  of  any  enamels  upon  which  it 
might  be  desirable  to  experiment. 

The  ten  enamels  are  those  given  in  the  "Taschenbuch 
fur  Keramiker,  1911, "x  pages  eighteen  and  nineteen.  It 
should  be  stated,  however,  that  some  changes  have  been 
made  in  the  milling  where  it  was  deemed  necessary,  and 
also  that  a  feldspar  high  in  silica  has  been  used  where 
the  formula  calls  for  pure  feldspar. 

All  the  materials,  except  the  borax  and  the  saltpeter, 
were  finely  ground.  Crystals  of  these  were  used.  The 
enamel  batches  were  weighed,  a  kilogram  at  a  time,  on 
a  balance  sensitive  to  one  hundredth  of  a  gram.  They 
were  then  very  thoroughly  mixed  and  were  smelted,  200 
grams  at  a  time,  in  a  gas-fired  crucible  furnace,2  at  tem- 
peratures varying  from  1050°  to  1200°  C.  This  smelting 
required  from  twelve  to  twenty-five  minutes  and,  as  is  the 
custom  in  practice,  the  molten  enamel  was  poured  into 
cold  water  to  facilitate  subsequent  grinding. 

The  resulting  frits  were  milled — after  drying — with 
the  required  amount  of  tin  oxide,  clay,  magnesia  and 


*  Reprinted  from  the  Transactions  of  the     American  Ceramic  Society.     Vol.   XIV. 

(Paper  read  at  Chicago,  111.,  Meeting,  March,  1912.) 

1  Published  by  the  Keramische  Rundschau,  Berlin,  N.  W.,  21,  Germany, 

*  See  E.  H.  Sargent's  Catalogue  No.  2098  for  illustration  and  description  of  this 

furnace. 

34 


water,  about  four  hundred  grams  at  a  time,  in  a  small 
porcelain  ball  mill.  (This  mill  is  manufactured  by  the 
Abbe  Engineering  Co.,  N.  Y.,  and  is  illustrated  on  page 
eleven  of  their  catalogue.)  The  time  required  for  mill- 
ing varied  from  3%  to  6%  hours. 

The  wet  enamel  from  the  mill  was  slushed  upon  minia- 
ture wash  basins  which  had  been  previously  coated  with 
a  good  cobalt  groundcoat.  After  drying  and  burning,  a 
second  coating  of  the  same  white  enamel  was  applied. 
Both  white  cover-coats  were  applied  as  thin  as  possible 
and  were  burned  in  the  regular  muffle  furnaces. 

These  dishes  were  then  tested  as  to  their  resistance 
against  corrosion  by  acetic  acid;  their  behavior  during 
rapid  expansion  and  contraction;  and  their  brittleness, 
elasticity  and  adhesiveness  under  punishment  by  impact; 
and  were  examined  as  to  their  opacity,  gloss,  etc.,  as  a 
finished  ware. 

METHODS  FOR  TESTING  THE  WARES 
Test  as  to  Corrosion  by  Acetic  Acid 

Each  dish  was  carefully  dried  and  weighed  correctly 
to  0.0001  gram;  and  15  cc.  of  20  per  cent,  acetic  acid8 
(20  per  cent,  by  volume  of  99.5  per  cent,  acid)  were 
measured  into  it.  It  was  then  placed  on  a  gas-fired  hot 
plate  and  boiled  to  dryness,  the  plate  being  so  regulated 
that  about  thirty  minutes  were  required  to  bring  the  ves- 
sel to  dryness.  The  enameled  dish  was  then  washed  out 
thoroughly  with  distilled  water,  rinsed,  dried  on  the  hot 
plate,  cooled  in  a  desiccator  and  again  weighed.  The 
difference  in  weight  is  the  amount  of  enamel  dissolved 
by  the  acid,  and  is  recorded  as  "Acid  Loss."  The  ten 
enamels  were  then  arranged  in  a  list  according  to  their 
relative  resistance  to  corrosion,  the  dish  losing  the  least 
being  first,  and  so  on.  The  position  of  each  enamel  in 
this  list  is  also  given  under  "Acid  Loss." 


'  This  has  been  shown  to  be  about  the  strongest  mixture  of  acetic  acid  and  water, 
as   measured  by  its  action   on  an  enamel.     See  page  — . 

35 


Tests  of  Adhesion  Under  Rapid  Expansion  and 
Contraction 

Test  1. — Twenty-five  cubic  centimeters  of  water 
were  heated  to  boiling  in  the  dish,  on  a  wire  gauze  over 
a  Bunsen  flame,  and  the  dish  was  then  plunged  into  cold 
water.  The  effect  of  this  treatment  on  the  enamel  was 
recorded. 

Test  2. — The  dish  from  Test  1  was  dried,  heated  on 
the  wire  gauze  over  the  Bunsen  flame  for  one  minute,  and 
then  plunged  into  cold  water  and  any  results  noted. 

Test  2l/%. — In  the  dish  from  Test  2  a  few  cubic  centi- 
meters of  water  were  boiled  away — over  the  Bunsen  flame 
as  in  the  other  two  tests — and  then  the  dish  was  allowed 
to  remain,  dry,  over  the  flame  for  one  minute  and  was 
again  plunged  into  cold  water.  (This  test  may  seem  a 
duplication  of  the  one  above.  It  is  not;  many  commercial 
wares  fail  with  this  test  as  it  is  especially  severe.) 

Test  3. — The  dried  dish  from  Test  2%  was  very 
gradually  heated  in  the  blast  flame  until  the  bottom  be- 
came red-hot.  The  results  of  this  rapid  expansion  were 
noted. 

Test  4. — While  the  dish  was  still  red-hot  from  Test  3 
it  was  plunged  into  cold  water  and  the  effect  of  this  rapid 
contraction  upon  the  enamel  coating  was  recorded. 

A  description  of  the  behavior  of  each  enamel  under 
these  tests  is  given  under  "Expansion  and  Contraction," 
and  it  is  to  be  noted  that  when  a  test  is  not  mentioned 
the  ware  was  unaffected  by  it.  Again  the  enamels  have 
been  listed,  this  time  according  to  their  adhesiveness 
under  rapid  changes  of  temperature,  and  their  position 
in  this  list  is  also  given  under  "Expansion  and  Contrac- 
tion." 

36 


Test  as  to  Adhesion  Under  Punishment  by  Impact 


A  testing  machine,  by  means  of  which  a  five-pound 
hammer  with  a  three-quarter  inch  rounded  head  can  be 
dropped  twenty  and  one-quarter  inches  onto  the  middle 
of  the  bottom  of  the  inverted  basin,  was  used.  The  sam- 
ple dishes  were  weighed  correctly  to  0.01  gram  before 
and  after  the  hammer  was  dropped  upon  them,  and  the 


TffANS.  AM.  CEff  SOC  Y0L.X/Y 


A  -^ 


A 


Jr= 


Impact  Testing  Machine. 

grams  loss  and  a  brief  description  of  the  effect  upon  the 
enamel  coating  is  recorded  under  "Loss  under  Hammer." 
As  before,  the  enamels  have  been  arranged  in  a  list  which 
shows  their  relative  adhesion  under  punishment  by  im- 
pact. 

Examination  as  to  Opacity 

The  finished  dishes  were  arranged  in  a  series  accord- 
ing to  their  opacity,  and  their  position  in  this  series  as 
well  as  other  details  as  to  their  appearance  are  given 
under  "Appearance  of  the  Ware." 

37 


Arrangement  of  the  Data 

It  is  the  custom  of  the  Lisk  Manufacturing  Com- 
pany's laboratory  to  make  a  complete  record  of  each 
enamel  on  a  single  sheet  of  special  form,  and  although 
this  cannot  be  followed  exactly  in  publishing  this  article, 
the  general  arrangement  and  form  of  report  will  be  re- 
tained. 

Immediately  under  the  heading  of  the  enamel  the 
batch  mix  in  percentages  and  the  calculated  graphic 
formula  is  given,  and  under  the  latter  the  oxygen  ratio 
and  the  ratio  of  the  silica  to  the  boric  anhydride 


Material  Formula  en  i 

Feldspar*  ......  0.45  NasO,  0.39  IfcO,  weight    ignition  pound 

0.06  CaO,  AhOs,  7.11  SiO«.  .602     1.43%  $0.0035 

Borax  .........  Na2O,  2BaOa,  lOHzO  ........  382  47.0  0.0375 

Quartz  .  .  .  .....  SiO*    .....................   60   .....  0.0025 

Cryolite  .......  2NasAlF6    .................  420  20.0  0.0600 

Soda  ..........  Na*0,  CO  ................  106  41.5  0.00^- 

Fluorspar  ......  CaF*     ....................    78  28.2  0.0045 

Calcite  ........  CaO,  CO    ................  100  43.9  0.0060 

Saltpeter   .....  .KX),  N2O»    ................  202  53.4  0.0525 

Garb,  magnesia.  .MgO,  CO   ................    84  52.1  0.0800 

Magnesia  ......  MgO    ....................   40   .....  0.1000 

Clay  ..........  AbOs,  2.8  SiOa,  1.6  H»0  .....  300  10.0  0.0100 

Tin  oxide   .....  SnO*    ....................  151   .....  0.4600 

4  Chemical  analysis  of  feldspar  : 


Per  cent. 

Silica 70.66 

Alumina   16.85 

Potash  (K2O)    5.98 

Soda  (Na2O,  by  diff.) 4.61 

Lime  (CaO)   0.52 

Carbon  dioxide 0.41 

Water    1.02 

100.00 


(SiO2/B2O3).  The  oxygen  ratio  is  given  considering 
A12O3  both  as  a  base  (ORb)  and  as  an  acid  (ORa).  Fol- 
lowing these  ratios  is  the  calculated  loss  on  smelting. 

38 


^si  *•* 


INSIDE: 


A  chemical  analysis  of  each  of  the  materials  used 
was  made,  and  from  them  the  following  formulas  were 
derived.  These  and  the  other  constants  given  in  the  table 
above  were  used  in  making  the  calculations. 

A  brief  description  of  the  action  of  each  enamel  dur- 
ing smelting  and  of  the  resulting  frit  is  given.  The  mill- 
ing follows  in  percentages  of  the  weight  of  frit  charged. 
Thus  "12  per  cent,  tin  oxide"  means  "12  grams  of  tin 
oxide  to  each  hundred  grams  of  frit."  Water  is  added 
to  each  milling  equal  to  50  per  cent,  of  the  weight  of 
the  frit. 

The  latter  part  of  the  record  of  each  enamel  needs 
no  further  explanation. 

The  Charts. — Figs.  2  and  3  show  a  method  of  ar- 
ranging all  the  data  in  regard  to  an  enamel  in  such  a 
form  that  it  may  very  easily  be  compared  with  any  other 
enamel.  The  data  of  the  enamels  may  be  separated  by 
cutting  along  the  horizontal  lines  of  the  chart  and  these 
slips  can  be  arranged  in  any  order  desired  for  making 
comparisons.  This  is  especially  desirable  in  a  series 
where  but  one  factor  is  changed  at  a  time  . 

The  Photographs  of  the  Dishes. — The  two  half-tones 
show  the  effect  of  the  "Hammer-  Test"  and  the  "Expan- 
sion and  Contraction  Tests"  upon  both  the  outside  and 
inside  enamel  coatings  of  the  ten  wares. 

Remarks. — The  types  of  these  enamels  are  so  differ- 
ent that  the  writer  will  not  try  to  draw  any  conclusions. 
In  figuring  the  graphic  formulas  the  customary  method 
has  been  used.  In  figuring  the  oxygen  ratio,  the  tin  oxide 
and  the  fluorine  have  been  ignored.  This  is  incorrect  in 
almost  every  case,  for  it  has  been  proved  by  experiment 
that  only  about  20  per  cent,  of  the  fluorine  is  driven  off, 
and  it  is  also  a  fact  that  some  of  the  tin  oxide  combines 
to  form  stannous  silicate.  This  is  especially  shown  in 
Enamel  X,  for  although  this  melted  enamel  contains  11.7 

43 


per  cent,  of  tin  oxide,  it  is  a  transparent  glaze.  Enamel 
II  also  illustrates  this,  for  although  its  oxygen  ration  is 
4.5  when  figured  in  the  ordinary  way,  it  is  one  of  the  most 
easily  smelted  of  the  enamels  under  discussion. 


Enamel  I 

Feldspar    38.6%  0.497  NasO       1  f  9  ci Q  a-n 

Quartz    19.0      0.186  KX)          I    ft  9qq  AI  o     J  n  9fi9  RO 

Borax    15.4      0.278  CaO  0.299  AW).    1  0.262  B.Qa 

Cryolite     11.7      0.039  MgO       J  l°'5ij 

Saltpeter     6.5 

Calcite     6.5      ORb  =  3.1  ORa  =  6.7  SiO^/B^Os  =  9.6 

Fluorspar    1.8 

Mg  carbonate  ....    1.0 

Loss  on  Smelting. — 17.34  per  cent. 

Milling. — Four  hours  with  12  per  cent,  tin  oxide,  7 
per  cent.  Vallendar  clay  and  %  per  cent,  magnesia. 

Smelting. — Smelted  at  about  1200°  C.,  hundred  gram 
batches  required  about  15  minutes.  The  melted  enamel 
is  quite  viscous  and  is  inclined  to  be  lumpy. 

The  Frit. — The  frit  is  fairly  opaque  but  is  translu- 
cent in  spots. 

Acid  Loss. — 0.0101  gram  (fifth  in  list). 

Expansion  and  Contraction. — This  ware  was  unaf- 
fected by  heating  to  redness  in  blast  flame  (Test  3)  and 
came  off  only  over  a  medium  sized  surface  on  the  outside 
and  a  comparatively  small  surface  on  the  inside  when 
plunged,  red-hot,  into  cold  water.  This  enamel  is  very 
adhesive,  according  to  this  test,  and  is  second  only  to 
Enamel  II. 

Loss  Under  Hammer. — This  was  1.07  grams,  and  the 
manner  in  which  the  enamel  comes  off  shows  it  to  be  of 
average  brittleness  and  elasticity.  It  is  placed  fifth  in 
the  list  according  to  this  test,  but  it  is  to  be  noticed  that 

44 


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all  the  enamels,  excepting  VIII,  which  is  much  the  best, 
and  IX  and  III,  which  are  much  the  worst,  stand  very 
close  together. 

Appearance  of  the  Ware. — This  ware  sets  a  very 
high  standard  in  its  appearance  and  is  much  more  opaque 
than  many  with  higher  tin  oxide  content.  In  fact,  it 
would  be  marketable  with  a  much  smaller  proportion  of 
this  oxide  added  at  the  mill,  and  with  this  change  would 
be  a  good  commercial  enamel.  As  it  stands,  it  is  fourth 
in  the  list,  according  to  opacity. 

Cost. — The  cost  of  the  materials  for  the  finished 
enamel  is  $6.70  per  hundred  pounds;  and  this  could  be 
reduced  by  using  less  potassium  nitrate,  and,  as  said  be- 
fore, by  using  less  tin  at  the  mill. 

Remarks. — If  the  cost  is  not  considered,  but  consid- 
ering everything  else,  this  is  the  second  best  enamel  of 
the  ten.  If  cost  is  considered,  it  is  the  very  best. 


Enamel   II 

Quartz 29.7%  0.563  NasO       )   (   1.636  SiO* 

Tin  oxide 24.0  0.131  KX)         £  ]   0.396  BsOs 

Borax    22.9  0.306  MgO       )   ( .0.525  SnO» 

Sodium  carbonate    11.7 

Saltpeter 8.0  OR  =  4.5  SiCb/BzOs  =  4.1 

Magnesia 3.7 


Loss  on  Smelting. — 19.89  per  cent. 

Milling. — Six  and  three-fourths  hours  with  4.3  per 
cent,  quartz,  2.1  per  cent,  tin  oxide  and  8  per  cent.  Val- 
lendar  clay.5 

Smelting. — Smelted  at  about  1200°  C.,  hundred 
gram  batches  required  about  15  minutes.  To  get  the 
maximum  opacity  it  was  necessary  to  mechanically  stir 
just  before  pouring.  The  viscosity  was  medium  and  melt 
was  free  from  lumps. 

The  Frit. — The  frit  was  extremely  opaque  and  quite 
hard  and  tough. 


6  Necessary  for  correct  slushing  but  not  given  in  original  directions. 

47 


Acid  Test. — The  acid  test  showed  this  enamel  to  be 
absolutely  unaffected  by  20  per  cent,  acetic  acid  solutions, 
and  thus  it  is  first  in  the  list  as  to  resistance  to  corrosion 
by  acid. 

Expansion  and  Contraction. — When  plunged,  red- 
hot,  into  cold  water  (Test  4)  this  enamel  came  off  over 
very  small  surfaces,  both  inside  and  outside,  and  in  such 
a  manner  that  it  is  easily  singled  out  as  the  most  adher- 
ent enamel  of  the  ten.  Few  enamels  have  ever  been 
tested  by  the  writer  that  have  withstood  sudden  changes 
of  temperature  as  well  as  this  one. 

Loss  Under  Hammer. — This  was  1.02  grams.  This 
enamel  is  of  average  brittleness  and  elasticity  and  is 
placed  third  in  the  list  as  to  adhesion  under  punishment 
by  impact,  but  an  examination  of  the  sample  used  for  this 
test  shows  that  it  is  not  as  well  suited  to  the  ground  coat 
as  is  Enamel  I. 

Appearance  of  Ware. — This  ware  is  very  opaque, 
and  it  certainly  should  be,  as  the  finished  enamel  contains 
something  like  32  per  cent,  of  tin  oxide.  It  is  second  in 
opacity  only  to  Enamel  VI,  which  contains  a  little  over 
23  per  cent,  of  tin  oxide  when  on  the  ware.  This  enamel 
is  so  opaque  that  it  may  be  put  on  in  very  thin  coatings. 
This  is  an  advantage,  as  the  thinner  the  enamel  is  applied 
the  more  durable  the  product. 

Cost. — The  cost  of  this  enamel  is  $15.07  per  hundred 
pounds,  and  this  would  make  it  entirely  impractical  to 
use  on  a  commercial  ware.  It  is  a  freak  enamel  in  every 
sense,  and  is  of  interest  on  this  account. 

Enamel  III 

Borax     30.0%  0.894  Na^O       1  f  2.217  SiO* 

Feldspar   22.0       0.097  IU)          1 0.147  AKM  0.632  BsQs 

Quartz     17.5       0.009  CaO  1 0.399  SnO 

Tin  oxide   15.0 

Sodium  carbonate  .  13.5      ORb  =  4.4  ORa  —  6.8  SiO/BsOs  =  3.5 
Saltpeter     2.0 

48 


Loss  on  Smelting.— 21.08  per  cent. 

Smelting. — Smelted  at  about  1200°  C.  for  15  minutes 
or  less ;  the  melt  pours  with  medium  viscosity. 

The  Frit. — The  frit  was  creamy-white  and  very 
opaque.  Some  of  the  tin  oxide  remained  in  suspension, 
but,  except  for  this,  the  frit  was  homogeneous. 

Milling.6 — Five  hours  with  10  per  cent.  Vallendar 
clay,  and  %  per  cent,  magnesium  oxide. 

Acid  Loss. — The  acid  loss  was  but  0.0016  gram.  This 
is  remarkably  low  and  places  this  enamel  second  in  the 
list  as  to  acid  resistance. 

Expansion  and  Contraction. — This  too  is  an  excellent 
enamel,  according  to  the  manner  in  which  it  withstands 
punishment  by  rapid  changes  of  temperature.  It  was 
unaffected  by  any  of  the  tests  up  to  Test  4  and  when 
plunged,  red-hot,  into  water  during  this  test  came  off  in 
flakes,  both  from  the  inside  and  outside  of  the  dish.  Very 
little  steel  was  laid  bare,  but  the  surface  of  the  ground 
coat  enamel  which  was  exposed  is  larger  than  on  either 
Enamel  I  or  Enamel  II.  This  enamel  is  placed  third  on 
the  list. 

Loss  Under  Hammer. — This  was  1.31  grams.  This 
shows  up  the  chief  fault  in  this  enamel — brittleness  and 
lack  of  elasticity — and  places  it  next  to  last  in  the  list, 
arranged  in  accordance  with  their  relative  ability  to  with- 
stand punishment  by  impact. 

Appearance  of  Ware. — Considering  the  fact  that  this 
enamel  contains  about  19  per  cent,  of  tin  oxide  when  on 
the  ware,  it  is  very  poor  in  opacity  indeed.  The  writer 
has  made  many  white  enamels  with  no  other  opacifier 
than  cryolite  that  were  more  opaque  than  this  one.  It  is 
fourth  from  the  poorest  among  these  ten. 


6  Original  directions  gave  no  milling. 

49 


Cost. — The  cost  of  this  enamel  is  $9.81  per  hundred 
pounds.  If  the  cost  is  not  considered,  this  enamel  stands 
fourth,  considering  all  its  properties. 

Enamel   IV 

Quartz 31.40%  0.834  Na*0       }  r  9  .71  a;n 

Feldspar 23.50  0.098  KX)         I  Q  24Q  AW)   I  J-Jg  ^ 

Cryolite    15.70  0.007  CaO  *24*  AK)'1  MH  5 

Borax    16.20  0.061  MgO       J 

Sodium  carbonate.  9.30 

Saltpeter     3.10  ORb  ss  3.4  ORa  =  6.8  SiOs/BaQs  =  9.5 

Magnesia    0.80 

Loss  on  Smelting. — 16.61  per  cent. 

Smelting. — Smelted  at  about  1100°  C.,  four  hundred 

gram  batches  required  15  minutes.     The  viscosity  of  the 
melt  was  medium. 

The  Frit. — The  frit  had  little,  if  any,  opacity  and 
with  a  smelting  of  18  minutes  became  a  clear  glass. 

Milling. — Four  hours  with  6.67  per  cent,  tin  oxide, 
4.44  per  cent.  Vallendar  clay,  and  %  per  cent,  magnesia. 

Acid  Loss. — 0.0033  gram,  placing  this  enamel  third 
on  the  list. 

Expansion  and  Contraction. — While  being  heated  to 
dryness  (Test  2i/2)  innumerable  "nail  chips"  flew  off, 
both  from  the  inside  and  outside  surface,  and  when 
heated  to  redness  in  the  blast  flame  (Test  3)  a  few  more 
came  off.  When  plunged  red  hot  into  cold  water  (Test 
4)  the  coatings  peeled  off  over  medium  sized  surfaces, 
leaving  the  ground  coat  almost  bare.  Notwithstanding 
the  apparent  adhesiveness  under  Tests  3  and  4,  the  utter 
failure  of  this  enamel  under  Test  2%  causes  it  to  be 
deemed  the  poorest  of  the  ten,  according  to  its  resistance 
to  punishment  by  rapid  changes  of  temperature. 

Loss  Under  Hammer. — This  was  1.07  grams;  and 
although  this  is  not  far  different  from  several  others,  the 

50 


manner  in  which  the  remaining  enamel  adhered  places 
this  ware  sixth  in  the  list. 

Appearance  of  the  Ware. — Although  this  enamel 
contains  but  eight  per  cent,  of  tin  oxide  in  its  finished 
coating,  it  is  opaque  enough  to  be  placed  fifth  in  the  list. 
The  gloss  is  quite  poor. 

Cost. — The  cost  of  this  enamel  is  $5.03  per  hundred 
pounds.  Its  final  rating  places  it  fifth  in  the  list. 

Enamel    V 

Feldspar    35.30%  0.504  NasO       ]  T2.447  SiO 

Quartz     20.50      0.176  KX)          >•  0.281  AkOsJ  0.284  BsQs 

Borax    16.80      0.320  CaO        J  10.636  Fa 

Cryolite 12.00 

Calcite 7.00     ORb  =  3.1  ORa  =  6.6  SiOa/BsO*  =  8.6 

Saltpeter     6.40 

Fluorspar    2.00 

Loss  on  Smelting. — 17.86  per  cent. 

Smelting. — Smelted  at  about  1100°  C.,  in  from  18  to 
20  minutes.  The  melt,  when  poured,  was  very  thick  and 
sticky.  This  mixture  is  inclined  to  melt  unevenly  and 
should  be  mechanically  stirred  for  best  results. 

The  Frit. — The  frit  has  a  translucent  white  color, 
fairly  good  for  the  amount  of  cryolite  it  contains.  It  is 
not  noticeably  hard  and  tough. 

Milling. — Five  hours  with  11.76  per  cent,  of  tin 
oxide,  5.88  per  cent,  of  Vallendar  clay,  and  14  per  cent, 
magnesia. 

Acid  Loss. — 0.0084  gram.  This  is  of  about  the  same 
acid  resistance  as  the  best  wares  on  the  market  and  is 
excelled  only  by  Enamels  I,  II  and  IV  in  this  list. 

Expansion  and  Contraction. — When  boiled  to  dry- 
ness  on  asbestos  gauze,  this  enamel  chipped  slightly 
(Test  2%)  but  was  not  further  affected  when  plunged 

51 


into  cold  water.  When  heated  to  redness  (Test  3)  more 
chips  flew  off  the  outside  and  the  inside  enamel  blistered 
somewhat.  When  plunged,  red  hot,  into  cold  water  ac- 
cording to  Test  6,  the  enamel  came  off  very  badly  from 
both  surfaces  of  the  dish,  and  much  steel  was  laid  bare. 
This  enamel  stands  sixth  according  to  this  test,  and  is 
typical  of  the  action  of  many  of  the  wares  on  the  market. 

Loss  Under  Hammer.  —  This  was  1.00  gram,  showing 
this  enamel  to  be  quite  elastic.  It  stands  next  to  the  best, 
according  to  this  test. 

Appearance  of  the  Ware.  —  This  ware  is  quite 
opaque,  standing  third  among  the  ten,  but  when  one  con- 
siders that  12  per  cent,  of  cryolite  was  used  in  the  smelt 
and  that  the  finished  enamel  contains  12  per  cent,  of  tin 
oxide,  he  comes  to  the  conclusion  that  much  of  the  color 
must  have  been  lost. 

Cost.  —  The  cost  of  this  enamel  is  $6.67  per  hundred 
pounds  and  its  final  rating  places  it  third  best,  when  all 
its  physical  properties  are  considered. 

Enamel  VI 

Feldspar    .......  32.00%          R  N    n       ]  r  1.558  SiO* 

Borax    .........  26.00      ™«     **>        L  I  0.415 


19g  AW)        . 
Tin  oxide    ......  11.00        'ft  1  °-452Fa 

Sodium  carbonate.  9.00      u'^4d  uau  1  0.222  SnCh 

Quartz     ........    8.00 

Fluorspar    ......    6.00     ORb  —  2.7  ORa  =  5.0  SiOa/BsOs  =  3.8 

Cryolite  ........    5.00 

Saltpeter  .......    3.00 

Loss  on  Smelting.  —  20.71  per  cent. 

Smelting.  —  Smelted  at  about  1150°  C.  in  from  20  to 
22  minutes.  The  viscosity  of  this  enamel  was  rather  low. 

The  Frit.  —  The  frit  was  creamy-white  and  quite 
opaque  but  inclined  to  be  non-homogeneous.  Threads  of 
this  enamel  were  brittle. 

52 


Milling.  —  Five  hours  with  9.3  per  cent,  tin  oxide,  7 
per  cent.  Vallendar  clay,  and  %  per  cent,  magnesia. 

Acid  Loss.  —  0.0190  gram,  placing  this  enamel  eighth 
on  that  list. 

Expansion  and  Contraction.  —  During  Test  3  a  few 
large  chips  came  off  while  the  dish  was  being  heated  to 
redness  in  the  blast  flame.  When  plunged  red-hot  into 
cold  water,  a  large  surface  of  the  ground  coat  was  laid 
bare  on  the  outside,  but  the  inside  was  affected  very  much 
less.  This  enamel  is  seventh  best,  according  to  this  test. 

Loss  Under  Hammer.  —  This  is  1.13  grams,  which  is 
the  average,  but  places  this  enamel  third  from  the  last 
when  listed  according  to  its  relative  resistance  to  punish- 
ment by  impact. 

Appearance  of  the  Ware.  —  This  is  the  best  appear- 
ing enamel  of  the  ten,  and  its  great  opacity  is  not  to  be 
wondered  at  when  we  consider  that  as  a  finished  enamel 
it  contains  about  23  per  cent,  of  tin  oxide.  The  gloss  is 
splendid. 

Cost.  —  The  cost  of  this  enamel  is  $11.10  per  hundred 
pounds;  but  as  much  more  oxide  of  tin  has  been  used 
than  is  necessary  for  even  a  very  high  grade  ware,  this 
could  be  greatly  reduced.  Considering  everything,  this 
is  the  sixth  best  enamel  of  the  ten. 

Enamel  VII 

Feldspar    .......  39.00%  0.500  NaaO       ^  f  2  525  SiO* 

0'. 


0.303  AM)     0.255 
Borax    .........  15.00      0.282  GaO  n  cqo  ™ 

Cryolite     .......  12.00      0.039  MgO       J 

Calcite  .........    7.00 

Saltpeter     ......    6.00      ORb  =  3.0  ORa  =  6.7  SiCb/BsO*  =  9.9 

Fluorspar    ......    1.00 

Mg  carbonate  .  .  .    1.00 

Loss  on  Smelting.  —  17.09  per  cent. 

Smelting.  —  Smelted  at  about   1200°    C.     The  melt 
poured  thin  and  somewhat  lumpy. 

53 


The  Frit.  —  The  frit  was  quite  translucent  and  non- 
homogeneous,  a  hard  glassy  frit. 

Milling.  —  Three  and  one-half  hours  with  11.1  per 
cent.  Vallendar  clay  and  1/4  per  cent,  magnesia. 

Acid  Loss.  —  0.0204  gram,  or  next  to  the  worst  in  the 
ten. 

Expansion  and  Contraction.  —  This  enamel  chipped 
somewhat  when  boiled  to  dryness  in  Test  21/2,  but  no 
more  chipping  was  observed  while  heating  to  redness  in 
blast  flame  (Test  3).  When  plunged,  red-hot,  into  cold 
water  (Test  4)  the  enamel  adhered  fairly  well,  especially 
on  the  inside,  but  the  failure  in/  Test  21/2  places  this 
enamel  next  to  the  poorest,  according  to  this  test. 

Loss  Under  Hammer.  —  This  was  1.06  grams  and  this 
ware  comes  fourth  as  to  its  adhesiveness  under  punish- 
ment by  impact. 

Appearance  of  Ware.  —  Considering  the  fact  that 
there  is  no  oxide  of  tin  in  this  enamel,  it  is  quite  opaque 
indeed  and  deserves  further  trial  with  tin  oxide  added  at 
the  mill.  Even  as  it  stands,  it  is  more  opaque  than  Enamel 
X,  which  contains  almost  12  per  cent,  of  tin  oxide.  It 
stands  next  to  the  last  in  the  list,  arranged  according  to 
the  relative  opacity  of  the  ware. 

Cost.  —  On  account  of  the  absence  of  tin  oxide  in  the 
make-up  of  this  enamel,  its  cost  is  but  $2.17  per  hundred 
pounds.  With  the  proper  addition  of  this  oxide  at  the 
mill,  this  enamel  would  cost  about  $5.00  per  hundred 
pounds.  Everything  except  the  cost  considered,  this 
enamel  is  rated  as  ninth  best. 

Enamel  VIII 

Feldspar    .......  38.40%  0  fifi1  N    n       }  r  1.509 


.  0  HI  i                  0.203  AM)3    0.463 

Tin  oxide   ......  13.90  n  99S  r_o                                 I  0.215  Fa 

Sodium  carbonate  11.30  1  0.293  SnO* 
Fluorspar    ......    5.30 

Saltpeter    ......    2.00  ORb  =  2.7  ORa  =  5.0  SiOs/BsO  —  3.3 

Quartz     ........    1.30 

54 


Loss  on  Smelting. — 20.87  per  cent. 

Smelting. — Smelted  at  about  1200°  C.  for  from  15 
to  18  minutes.  The  viscosity  was  rather  low.  Although 
the  melting  point  of  this  enamel  is  low,  it  was  difficult  to 
drive  off  all  the  CO2. 

The  Frit. — The  frit  was  creamy  and  very  opaque, 
but  rather  brittle. 

Milling. — Four  hours  with  7.87  per  cent,  tin  oxide, 
4.5  per  cen.  Vallendar  clay,  and  ^4  Per  cent,  magnesia. 

Acid  Loss. — 0.0353  gram.  This  is  entirely  too  high 
for  a  cooking  utensil  and  places  this  ware  last  in  the  list 
as  to  its  resistance  to  corrosion  by  acetic  acid. 

Expansion  and  Contraction. — While  heating  this  dish 
to  redness,  a  few  chips  flew  off  and  when  plunged,  red- 
hot,  into  cold  water  (Test  4)  the  enamel  flaked  off  over 
quite  a  large  surface,  but  only  to  the  ground  coat  and 
even  this  was  fairly  well  covered  by  the  adhering  cover 
coat.  This  ware  stands  fourth  according  to  this  test. 

Loss  Under  Hammer. — This  was  0.56  gram,  so  that 
according  to  this  test  the  enamel  is  very  excellent  indeed. 
It  stands  punishment  by  impact  better  than  any  of  the 
rest. 

Appearance  of  Ware. — The  opacity  of  this  ware  is 
very  low,  considering  the  fact  that  it  contains  25%  per 
cent,  of  tin  oxide.  It  stands  sixth  when  listed  according 
to  opacity. 

Cost. — The  cost  of  this  ware  is  $21.08  per  hundred 
pounds.  This  is  the  most  expensive  of  the  wares,  except 
one,  and  yet  it  stands  sixth  according  to  opacity  and 
eighth  when  everything  is  considered. 

55 


Enamel  IX 

Quartz    35.30%  0.670  Na^O 

Borax    20.50  0.062  K,O  22g  ^ 

Cryolite     19.40  0.005  CaO  1  n  Rt>,  ^ 

Feldspar 17.70  0.263  MgO 

Magnesia    3.50 

Sodium  carbonate  1.80  ORb  =  3.4  ORa  =  6.5  SiO*/BiO'  =  7.4 

Saltpeter     1.80 

Loss  on  Smelting. — 15.48  per  cent. 

Smelting. — Smelted  at  about  1200°  C.  for  from  15  to 
18  minutes.  This  enamel  was  difficult  to  pour  from  the 
crucible.  The  enamel  was  quite  viscous  and  lumpy. 

The  Frit. — The  frit  was  very  hard  and,  although 
quite  opaque,  was  translucent  in  spots. 

Milling.7 — Three  and  a  half  hours  with  10  per  cent. 
Vallendar  clay  and  %  per  cent,  magnesia. 

Acid  Loss. — 0.0159  gram,  or  seventh  in  the  list  of 
ten  enamels. 

Expansion  and  Contraction. — When  plunged,  red- 
hot,  into  cold  water  (Test  4)  this  enamel  came  off  over  a 
large  surface  on  the  outside  and  a  small  surface  on  the 
inside  of  the  dish.  The  steel  was  laid  bare  in  many  places. 
In  the  list  of  wares,  arranged  according  to  their  resistance 
to  punishment  by  change  of  temperature,  this  enamel 
stands  eighth,  as  it  scaled  slightly  during  Test  2%  when 
water  was  boiled  to  dryness  in  it. 

Loss  Under  Hammer. — This  was  1.42  grams,  which 
is  more  than  any  of  the  other  dishes  lost,  and  places  this 
enamel  last  in  the  list. 

Appearance  of  Ware. — This  enamel  is  remarkable  in 
its  opacity,  all  of  which  comes  from  the  cryolite  and  clay. 
It  contains  no  tin  oxide  and  stands  eighth  in  the  list  ac- 
cording to  opacity. 


7  Milling  not  given  in  original  directions. 

56 


Cost. — The  cost  is  but  $2.87  per  hundred  pounds. 
With  sufficient  oxide  added  at  the  mill  to  bring  this  up  to 
a  remarkable  standard,  this  enamel  would  cost  about 
$5.50  per  hundred  pounds.  Considering  everything,  this 
is  the  poorest  enamel  of  the  ten. 

Enamel   X 

Feldspar    45.70%  0.841  Na*0       ]  T2.013  SiO* 

Borax    32.00      0.142  KX)          f  0.283  AkOH  0.625  B2Os 

Sodium  carbonate  11.40      0.017  CaO        J  1 0.227  SnO 

Tin  oxide 9.20 

Saltpeter     1.70      ORb  ==  3.2  ORa  —  6.8  SiO/BaO«  =  3.2 

Loss  on  Smelting. — 21.33  per  cent. 

Smelting. — Smelted  at  about  1050°  C.  for  20  minutes; 
this  enamel  became  transparent,  although  it  contains  9.2 
per  cent,  tin  oxide.  Its  viscosity  was  medium. 

The  Frit. — The  frit  was  a  colorless  glass,  compara- 
tively hard  and  quite  tough. 

Milling. — Four  and  one-fourth  hours  with  6.4  per 
cent.  Vallendar  clay  and  %  per  cent,  magnesia. 

Acid  Loss. — 0.0119  gram,  placing  this  enamel  sixth 
in  the  list. 

Expansion  and  Contraction. — While  heating  to  red- 
ness in  the  blast  flame,  the  enamel  bubbled  slightly,  and 
when  plunged,  red-hot,  into  cold  water,  came  off  to  the 
steel  over  a  small  surface  on  the  inside  and  a  larger  sur- 
face on  the  outside.  This  enamel  stands  fifth,  according 
to  this  test. 

Loss  Under  Hammer. — This  was  1.09  grams,  which 
places  this  cover  coat  seventh  in  the  list. 

Appearance  of  Ware. — Although  this  enamel  con- 
tains 11.7  per  cent,  tin  oxide,  it  stands  last  in  opacity,  be- 
ing nothing  more  nor  less  than  a  clear  glass. 

Cost. — The  cost  of  this  enamel  is  $7.01  per  hundred 
pounds. 

67 


Discussion 

MR.  RANKIN:  Mr.  Landrum,  I  would  like  to  ask 
if  you  have  ever  made  any  experiments  in  the  line  of  sub- 
stituting sodium  nitrate  for  potassium  nitrate? 

MR.  LANDRUM:  I  have  made  experiments  on  a 
small  scale  and  a  large  scale.  The  substitution  of  sodium 
nitrate  for  potassium  nitrate  is  successful  only  where  you 
can  make  routine  analyses  of  the  sodium  nitrate.  Sodium 
nitrate  takes  up  water  from  the  air,  and  thus  varies  in 
strength.  In  the  sheet  steel  enameling  industry,  the  va- 
riation of  water  content  will  spoil  the  enamel  unless  this 
is  taken  into  account. 

I  worked  in  one  place  where  they  determine  this  very 
nicely  by  weighing  about  ten  or  fifteen  pounds  and  then 
drying  and  reweighing  it,  thus  getting  results  which  were 
as  accurate  as  taking  a  smaller  sample  and  testing  it  in 
the  laboratory. 

MR.  STALEY:  I  wish  to  say  that  I  consider  this  a 
very  able  paper. 

The  Germans  do  not  use  the  empirical  formula  in 
their  enamel  industries  to  any  large  extent.  They  publish 
their  results  in  percentage  of  the  various  oxides.  When 
it  comes  to  fluorides,  they  publish  their  results  in  percent- 
age of  the  various  fluorides.  I  think  that  is  a  fairly  good 
way.  In  my  own  papers,  I  prefer  to  consider  the  melted 
weights  of  the  various  minerals;  consider  the  feldspar, 
for  instance,  as  feldspar  rather  than  as  split  up  into  the 
oxides.  The  method  I  use  is  very  similar  to  that  of  the 
Germans.  Mr.  Landrum  advocates  the  use  of  empirical 
formulas  in  connection  with  batch  weights.  This  diverg- 
ence in  methods  of  calculation  shows  very  nicely  that, 
provided  a  man  works  in  a  systematic  manner  and  has 
enough  experience,  he  can  get  results  from  a  variety  of 
methods  of  calculation. 

Enamels  III  and  X  are  two  cases  where  there  are 
high  sodium  and  potassium  oxides  and  practically  no 

58 


other  basic  oxide.  I  believe  that  early  in  the  history  of 
this  Society  Mr.  Burt  gave  the  results  of  some  experiments 
in  which  he  showed  that  you  can  melt  tin  oxide  and 
sodium  carbonate,  or  tin  oxide  and  potassium  carbonate, 
together  and  get  a  clear  glass.  It  is  known  that  there 
are  sodium  stannates  and  potassium  stannates  in  existence 
which  are  translucent.  I  think  it  is  more  plausible  to  say 
that  in  a  material  as  basic  as  enamel  the  loss  in  opacity 
is  due  to  the  fact  that  the  potash  and  soda  are  high  rather 
than  to  attribute  the  poor  opacity  to  any  hypothetical 
effect  that  the  alkaline  earths  have  in  preventing  the  tin 
from  forming  stannous  silicate.  I  have  always  found  that, 
with  a  given  amount  of  tin  oxide,  when  sodium  and  po- 
tassium run  up  the  opacity  decreases.  To  verify  Mr. 
Landrum,  I  find  that  increasing  calcium  or  barium  oxide 
increases  the  opacity.  To  my  mind  this  means  simply 
that  opacity  was  increased  by  decreasing  the  percentage 
of  sodium  and  potassium. 

MR.  PURDY :  I  would  like  to  ask  Mr.  Landrum  if 
it  makes  any  difference  in  the  power  of  tin  oxide  to  pro- 
duce opacity,  whether  you  frit  it  or  use  it  raw? 

MR.  LANDRUM :  Yes,  there  is  a  very  marked  dif- 
ference. This  has  already  been  brought  out  in  the  Trans- 
actions. It  never  pays  to  put  tin  oxide  in  the  smelt  for 
opacity. 

I  have  found,  however,  that  it  is  good  practice  to  put 
a  small  amount  of  tin  oxide  in  the  smelt  for  gloss.  In  this 
case  you  get  no  opacity  from  the  tin  oxide.  For  maximum 
color,  the  tin  oxide  should  be  added  at  the  mill. 


59 


THE  NECESSITY  OF  COBALT  OXIDE  IN  GROUND- 
COAT  ENAMELS  FOR  SHEET  STEEL* 

There  has  been  a  great  deal  of  discussion  recently 
in  German  ceramic  literature  over  the  function  of  the 
ground  coat  and  especially  as  to  the  necessity  of  cobalt 
being  present  in  such  an  enamel.  As  the  durability  of  an 
enameled  ware  is  primarily  dependent  upon  the  physical 
properties  of  this  fundamental  coating,  it  might  be  well 
to  review  what  has  been  said  upon  the  subject. 

In  the  Transactions  of  the  American  Ceramic  Society, 
XI,  p.  115,  J.  B.  Shaw  says  that  cobalt-containing  grounds 
have  the  advantage  that  they  change  color  during  burn- 
ing, the  iron  taken  up  from  the  steel  destroying  the  blue 
cobalt  color.  "The  ground  coat  is  considered  well  burnt 
when  the  blue  color  is  no  longer  visible.  It  seems  to  be 
quite  generally  believed  that  CoO  has  a  great  affinity  for 
iron  and  that  a  good  ground  coat  cannot  be  made  without 
using  CoO."  Shaw  goes  on  to  say  that  from  his  experi- 
ments along  this  line  he  feels  perfectly  safe  in  stating 
that  this  belief  is  ungrounded. 

About  the  only  other  time  that  this  subject  is  men- 
tioned in  the  Transactions  is  by  J.  H.  Coe,  Volume  XIII, 
p.  549,  and  he  states  that  the  value  of  cobalt  oxide  in  the 
ground  coat  for  cast  iron  is  doubtful. 

Dr.  Grunwald  in  his  book  "Enameling  on  Iron  and 
Steel,"  p.  22,  says:  "Cobalt  oxide  possesses  valuable 
physical  characteristics  which  make  it  suitable  for  the 
preparation  of  ground  (coat)  enamels,  for  these  derive 
the  property  that  their  coefficients  of  expansion  are  as 
near  as  possible  the  same  as  sheet  iron."  This  is  disputed 
by  M.  Mayer  and  B.  Havas1  who  find  that  ground  coat 


*Reprinted   from  the  Transactions  of  the  American   Ceramic  Society.     Vol.   XIV. 
(Paper  read  at  Chicago    111.,   Meeting,  March,  1912.) 
1  Chem.  Ztg.  Vol.  XXXIII,  p.  1314. 

60 


enamels  have  a  much  lower  coefficient  of  expansion  than 
that  of  sheet  steel. 

Dr.  Vondracek,  in  the  Sprechsaal,  1909,  No.  14, 
seems  to  have  first  propounded  the  theory  of  the  function 
of  cobalt  in  a  ground-coat  enamel  which  is  most  popular 
at  present.  He  considers  that  the  iron,  at  the  melting 
temperature  of  the  ground  coat,  is  oxidized  at  the  ex- 
pense of  the  cobalt  oxide  and  that  the  latter,  or  rather 
the  cobalt  silicate,  is  changed  to  a  compound  of  lower 
oxygen  content,  or  is  even  reduced  to  the  metal.  As  a 
result  of  this,  the  clean  surface  of  the  iron  is  attacked  so 
that  the  enamel  joins  very  intimately  with  the  metal  and 
the  danger  of  the  chipping  off  of  the  enamel  coats  is 
lessened.  In  another  place,  Dr.  Vondracek,  although  he 
repeats  that  cobalt  improves  the  adhesiveness  of  enamels, 
says :  "I  have,  notwithstanding,  often  obtained  a  very  ad- 
hesive ground-coat  enamel  without  using  cobalt  oxide."2 

Philip  Eyer  in  his  book  "Die  Eisenemailierung,"  pp. 
10-12,  says:  "The  idea  of  adding  cobalt  oxide  to  the  glaze 
so  that  it  will  go  into  combination  with  the  iron  is  faulty, 
for  a  good,  adherent  ground-glaze  can  be  prepared  with- 
out the  use  of  that  oxide.  However,  the  application  of 
such  a  ground  coat  is  impossible  in  practice."  Also  in 
writing  of  cast-iron  enamels  in  the  "Glashutte,"  Vol. 
XLI,  pp.  737-8,  764-5,  he  says  that  cobalt  and  nickel  are 
necessary  as  they  form  a  weak  alloy  with  the  iron. 

C.  Tostman,  in  the  Keramische  Rundschau,  XIX,  pp. 
5,  65  and  107,  discusses  this  subject  and  emphasizes 
especially,  what  is,  in  the  writer's  opinion,  the  best  argu- 
ment as  to  the  necessity  of  cobalt  in  a  ground  coat.  He 
agrees  with  Shaw  that  cobalt  acts  as  an  indicator  for  cor- 
rectly burning  the  enamel.  He  says  in  part: 

"Only  in  cobalt  oxide  grounds  does  a  blue  color  appear  on 
smelting.  If  one  should  discontinue  the  heating  just  at  this  point, 
it  would  not  adhere  firmly  enough  to  the  steel,  even  though  it  had 
already  become  molten  and  glass-like.  One  can  also  burn  it  so  long 

2  See  Chem.  Ztg.,  XXX,  575-7. 

61 


that  the  color  becomes  black.  Now  how  is  this  (definite)  color 
change,  which  is  so  markedly  essential  for  a  proper  adhesion,  to  be 
explained?  The  only  explanation  I  find  for  it  is  that  the  enamel  has 
taken  up  the  iron  from  the  surface  (of  the  black  shape)  in  some 
form  of  oxidation." 

He  goes  on  to  state  that  while  this  oxygen  might 
come  from  the  air  in  the  muffle,  it  is  more  probable  that 
it  is  given  up  by  the  oxide  of  cobalt,  which  is  in  turn  re- 
duced to  metal.  "These  small  amounts  of  very  finely  di- 
vided metallic  cobalt  could  then  perhaps  form  a  very 
porous  alloy  with  the  iron  on  the  surface  of  the  shape. 
To  this,  the  enamel  would  be  able  to  adhere  firmly,  while 
the  silicate  flux  would  take  the  place  of  the  cobalt  which 
alloyed  with  the  iron."  He  gives  as  an  argument  that  this 
oxygen  is  furnished  to  the  iron  by  the  cobalt  and  not 
from  any  other  source,  the  fact  that  in  ground  coats, 
which  are  not  colored  by  cobalt,  "an  exceedingly  smaller 
change  of  color  takes  place  during  the  burning."  He 
also  mentions  the  fact  that  the  addition  of  borax  to  an 
enamel  causes  it  to  chip  and  the  further  addition  of  co- 
balt oxide  seems  to  correct  this. 

Dr.  Bela  Havas3  replies  to  Tostman  that  he  agrees 
with  him  that  the  cobalt  silicate  in  the  ground  coat  is  re- 
duced to  a  lower  stage  of  oxidation  and,  as  previously 
published  by  him  in  cooperation  with  M.  Mayer,4  this  is 
indicated  by  the  change  of  color  of  the  enamel  coating 
from  blue  to  green.  However,  he  states  that  it  is  im- 
probable that  the  reduction  of  the  cobalt  silicate  at  the 
temperatures  involved  would  go  far  enough  to  produce 
metallic  cobalt. 

The  writer  has  no  new  theories  to  offer,  but  he  is  very 
strongly  of  the  opinion  that  cobalt  is  a  necessary  ingredi- 
ent in  a  successful  ground  coat  for  two  reasons,  which 
have  been  given  above : 

First,  it  is  an  excellent  indicator  which  will  inform 
the  "burner"  exactly  the  point  at  which  his  charge  of 
ware  is  correctly  burned. 


'Sprechsaal    XLIV    72-3. 
•Ibid.,  XLHI,  727-9. 

62 


Fig.  1 


Second,  whatever  may  be  the  reason,  the  fact  re- 
mains that  cobalt  grounds  adhere  more  firmly  to  the  steel 
than  those  not  containing  this  metal,  and  it  is  the  opin- 
ion of  the  writer  that  any  non-cobalt  ground  coat  can  be 
improved  in  its  adhesive  properties  by  the  correct  addi- 
tion of  cobalt  to  its  formula. 

To  illustrate  this  a  ground  coat  was  prepared  which 
is  practically  a  transparent  glaze.  When  it  is  coated  on 
a  piece  of  ware  the  bright  steel  surface  shows  through 
the  glaze  and  makes  this  appear  a  very  light  colored 

coating  (see  Fig.  I,  1).  The  composition  is  practically 
the  same  as  that  of  the  Mayer  and  Havas  ground  No.  1 
as  given  in  the  Sprechsaal,  1909,  No.  34. 

M-H.     Ground  Coat  Number  One5 

Batch  mix  Graphic  formula 

Feldspar    .......  36.34%  0.642  Na*0      ^  r 

Borax    .........  35.64  0.0802KX)  2.256  SiO 

Quartz    ........  14.38  0.243CaO          Y  0.204  AUO^  0.231  F* 

Soda    ..........    7.42  0.025  MnO  0.629  BsOs 

Fluorspar    ......    5.34  0.010  CoO 

Manganese   oxide.  0.65 

Cobalt  oxide  ____    0.23  ORb  4.0,  ORb  7.0,  SiOa/B'O*  3.6 

Milled  with  6  per  cent,  clay  and  2Vfc  per  cent,  dis- 
solved borax. 

A  cobalt  ground  coat  has  been  prepared  which  has 
the  same  chemical  composition  except  that  0.03  equiva- 
lent part  of  CaO  has  been  replaced  by  0.03  equivalent 
part  of  CoO  (see  Fig.  I,  2).  This  enamel  has  been  made 
as  follows  : 

Cobalt  Ground  Coat5 

Batch  mix  Graphic  formula 

Feldspar    .......  36.42%  0.642  Na*O       1  2.260  SiO 

Borax    .........  35.54  0.080  IfcO 

Quartz     ........  14.38  0.213  CaO         fO?203  AhOJ  0.628  BsQa 

Soda    .  .........    7.42  0.040  CoO 

Fluorspar    ......    4.64  0.025  MnO  1  0.201  Fa 

Manganese  oxide.    0.65 

Cobalt  oxide  ____    0.95  ORb  4.0,  ORa  7.0,  SiOs/B^Os  3.6 


5  The  same  materials  and  method  of  manufacturing  and  a  similar  arrangement  of 
data  have  been  used  as  in  "Comparison  of  Ten  White  Enamels  for  Sheet  Steel," 
this  volume. 

65 


Milled  with  6  per  cent,  clay  and  2%  per  cent,  dis- 
solved borax. 

Each  of  these  enamels  has  been  coated  with  two 
white  cover  coats  and  then  tested  under  the  hammer  (see 
article  on  white  enamels),  and  it  is  to  be  noticed  that  the 
non-cobalt  ground  coat  leaves  the  steel  entirely  bright 
and  bare  (see  Fig.  I,  3),  while  the  one  containing  cobalt 
still  adheres  in  concentric  ridges  (see  Fig.  I,  4).  It  is 
very  evident  that  the  cobalt  must  cause  this  extra  ad- 
hesiveness. 

Discussion 

MR.  LANDRUM :  As  an  example  of  the  reduction 
of  a  metal  oxide  (or  silicate)  in  an  enamel  coating  by  the 
steel  of  the  shape  it  may  be  interesting  to  examine  a 
sample  dish  coated  with  the  following  enamel : 

0.451  Na*O       ]  r  0.886  SiO* 

0.019  KX) 

0.123  CaO  0.111  AK>«    4  0.282  B*0* 

0.285  ZnO 

0.122  CuO  L  0.123  F* 

Milled  with  6%  per  cent.  clay. 

This  enamel  when  used  as  a  cover  coat  (separated 
from  the  steel  by  a  ground-coat  enamel)  is  green  but 
when  applied  directly  to  the  steel  becomes  red  through 
the  reduction  of  the  copper  compound.  It  may  be  ob- 
served on  the  sample  which  has  been  dented  in  the  test- 
ing machine  that  some  of  the  copper  compound  has  been 
reduced  to  the  metal  and  that  this  is  plated  on  the  steel 
surface. 

MR.  PURDY :  You  have  tried  oxides  other  than  co- 
balt? Have  you  tried  nickel,  for  instance? 

MR.  LANDRUM :  I  have  tried  oxide  of  nickel  and 
it  works  fairly  well,  but  does  not  promote  adhesiveness 
to  as  great  a  degree  as  does  the  oxide  of  cobalt.  It  is 
best  used  in  combination  with  that  oxide. 

66 


MR.  PURDY :  There  is  no  actual  oxygen  for  it  to 
give  up. 

MR.  LANDRUM :  We  have  nickelic  and  nickelous 
compounds,  and  the  change  may  be  from  one  to  the  other 
and  not  necessarily  a  change  of  the  oxides ;  then,  too,  the 
conclusion  might  be  drawn  that  the  reduction  is  to  metal- 
lic nickel.  In  the  case  of  the  enamels  under  discussion, 
it  is  easy  to  see  that  the  one  containing  cobalt  (see  vessel 
4  in  illustration)  does  adhere  to  the  steel  after  being 
dented  while  the  one  which  does  not  contain  cobalt  (ves- 
sel 3)  does  not  adhere  but  leaves  the  steel  surface  bright. 

PROF.  STALEY:  You  will  have  to  look  at  it  with 
a  microscope. 

MR.  LANDRUM :  I  have  examined  this  and  other 
cobalt  grounds  under  the  microscope  and  have  not  been 
able  to  see  any  evidence  of  an  alloy  being  present.  The 
dark  particles  remaining  after  the  dish  is  dented  have  a 
gloss  that  would  lead  one  to  think  that  they  are  particles 
of  the  glaze  rather  than  of  metal.  Microscopic  examina- 
tion is  difficult  as  it  is  practically  impossible  to  get  a  good 
cross  section  of  an  enameled  steel  sheet. 

PROF.  STALEY :  In  other  words,  this  alloy  theory 
is  used  just  because  it  fits  in — because  it  is  within  reason? 

MR.  LANDRUM:  Yes,  and  even  then  there  is  a 
doubt  that  it  is  within  reason  at  enameling  temperatures. 

MR.  PURDY:  In  our  transactions  I  stated  as  my 
opinion  that  cobalt  in  the  ground  coat  merely  furnished 
a  mechanical  means  of  holding  the  enamel  onto  the  iron. 
It  is  easy  to  enamel  most  metals  directly,  but  very  difficult 
to  enamel  iron.  The  cobalt  is  merely  suspended  in  the 
ground  coat  furnishing  the  required  easily  enameled  "go 
between." 

MR.  LANDRUM :  This  may  be  true  and  would  be 
a  good  explanation.  There  is  an  interaction  between  the 
iron  and  the  enamel  when  you  have  cobalt  present ;  when 


you  do  not  have  cobalt  present  there  is  no  interaction. 
Sample  1  (see  illustration),  which  is  enameled  with  the 
non-cobalt  ground  coat,  is  nicely  covered ;  but  under  im- 
pact the  enamel  comes  off,  leaving  the  bright  steel  (see 
dish  3).  Sample  2  is  covered  with  the  same  enamel  with 
1  per  cent,  of  oxide  of  cobalt  added,  and  when  subjected 
to  the  same  blow,  adheres  firmly  in  ridges,  barely  expos- 
ing the  steel  between  them  (see  dish  4).  Samples  Nos. 
5  and  6  also  show  how  the  adhesiveness,  under  punish- 
ment by  rapid  changes  of  temperature,  is  promoted  by 
the  addition  of  oxide  of  cobalt.  Both  have  been  heated 
red  hot  and  plunged  into  cold  water.  Number  5,  whose 
fundamental  coating  contains  no  cobalt,  peels  off  clean, 
to  the  steel,  while  6,  whose  fundamental  coating  is  the 
cobalt  ground,  exposes  no  steel  at  all. 

PROF.  STALEY:  I  would  like  to  have  Mr.  Landrum 
prove  that  there  is  an  interaction  between  the  ground 
coat  and  the  iron  when  cobalt  is  present  and  no  interaction 
when  cobalt  is  absent.  I  would  also  like  to  see  him  de- 
monstrate the  presence  of  a  porous  alloy  between  the 
enamel  and  iron.  In  regard  to  what  Prof.  Purdy  has  said, 
I  would  like  to  know  on  what  evidence  he  bases  his  state- 
ment that  cobalt  is  merely  suspended  in  the  ground  coat 
and,  furthermore,  to  explain  the  mechanics  of  just  how 
such  a  suspension,  if  it  should  exist,  would  make  a  more 
tenacious  ground  coat.  We  have  one  fact,  namely,  that 
the  addition  of  cobalt  to  a  ground  coat  for  sheet  steel 
enamels  makes  it  a  better  ground  coat.  This  is  admir- 
ably shown  by  Mr.  Landrum's  paper.  Beyond  this  one 
fact,  we  can  merely  speculate  until  some  one  produces 
some  evidence. 

MR.  LANDRUM :  We  are  merely  speculating  as  to 
the  "mechanics"  of  the  action  of  the  cobalt,  but  I  believe 
that  these  samples  show  to  the  naked  eye  that  there  has 
been  an  interaction  between  the  steel  and  the  cobalt- 
containing  enamel,  and  that  there  has  not  been  such  an 
interaction  in  the  case  of  the  non-cobalt  enamel.  It  might 


throw  light  on  the  subject  to  consider  the  fact  that  even 
a  cobalt-containing  ground  coat  will  not  adhere  well  to 
a  steel  surface  unless  that  surface  has  been  made  rough, 
or  porous  or  crystallized  by  pickling,  sand-blasting,  or 
annealing.  It  may  be  that  the  enamel  simply  sinks  down 
into  the  pores  of  the  steel,  but  the  question  is:  Why 
should  an  enamel  have  to  contain  cobalt  to  do  this?  Now 
if  some  one  has  the  facilities  to  make  a  cross-section  of  a 
piece  of  enameled  steel,  I  would  like  to  see  it.  Such  a 
section  might  explain  this  matter. 


69 


METHODS  OF  ANALYSIS  FOR  ENAMEL  AND 
ENAMEL  RAW  MATERIALS* 

Introduction.1  The  fact  that  practically  nothing  has 
been  published  on  the  above  subject,  and  the  remem- 
brance of  the  many  long  hours  spent  in  digging  out  these 
methods  and  adapting  them  to  enamels  and  enamel  raw 
materials,  has  led  the  author  to  put  them  in  this  form  for 
others  who  might  use  them.  While  he  claims  little  origi- 
nality in  the  methods  themselves,  he  does  claim  originality 
in  the  adaptations  here  given.  Each  and  every  one  of 
these  methods  has  been  thoroughly  tried  out,  either  in 
the  laboratory  of  the  Columbian  Enameling  and  Stamp- 
ing Company,  at  Terre  Haute,  Ind.,  or  in  the  chemical 
laboratories  of  the  University  of  Kansas. 

PART  I. 
The  Analysis  of  an  Enamel 

The  analysis  of  an  enamel  presents  one  of  the  most 
difficult  and  complicated  problems  with  which  the  an- 
alyst comes  in  contact.  An  enamel  is  generally  an  in- 
soluble silicate  containing  besides  silica,  iron,  alumina, 
calcium,  magnesium  and  the  alkalies,  generally  boron, 
fluorine,  manganese,  cobalt,  antimony  and  tin,  and  some- 
times phosphorus  and  lead.  Before  attempting  the  quan- 
titative analysis  of  any  enamel  a  thorough  qualitative 
analysis  should  be  run,  and  this  will  enable  one  to  choose 

*  Reprinted  from  Vol.  XII,  page  144,  Transactions  of  American  Ceramic  Society.  (Read 
at  Pittsburgh  Meeting,  February,  1910. 

1  This  paper  was  prepared  as  a  thesis  for  the  master's  degree  at  Rose  Polytechnic 
Institute.  The  author  desires  to  render  thanks  to  Dr.  W.  A.  Noyes  and  Dr.  John 
White,  his  former  instructors,  for  advice  freely  given,  and  to  Dr.  E.  H.  S.  Bailey 
and  Dr.  H.  P.  Cady  for  suggestions  offered.  Methods,  especially  from  the  following 
sources,  have  been  freely  used,  and  adapted  to  the  specific  uses  herein  described ; 
Treadwell  and  Hall's  "Analytical  Chemistry"  ;  Classen's  "Ausgewahlte  Methoden  der 
Analytischen  Chemie"  ;  Button's  "Volumetric  Analysis"  ;  Lunge  and  Keane's  "Techni- 
cal Methods  of  Chemical  Analysis";  "Methods  of  Agricultural  Analysis"  (Bui.  107, 
U.  S.  Dep't  of  Agric.)  ;  Hillebrand's  "Analysis  of  Silicate  Rocks"  (U.  S.  Geol.  Survey 
Bui.  305)  ;  and  the  files  of  the  Journals  of  the  various  Chemical  Societies. 

70 


a  quantitative  separation.  One  of  the  most  important 
aids  to  a  correct  analysis  is  a  thorough  grinding.  The 
sample  should  be  ground  to  an  almost  impalpable  powder, 
and  every  conceivable  precaution  for  accuracy  taken. 

The  analysis  of  a  sample  of  enamel  to  be  taken  from 
a  piece  of  ware  involves  an  extra  difficulty.  The  coating 
of  enamel  almost  always  consists  of  two  or  more  layers — 
the  lower  a  large  ground  coat,  and  the  upper  ones  white 
or  colored  enamels.  For  an  illuminating  analysis  these 
must  be  separated.  The  author  has  found  the  following 
method  of  V.  de  Luyeres1  good  for  doing  this:  The  sur- 
face is  scratched  lightly  with  a  piece  of  emery  cloth  or  a 
file,  and  a  coating  of  gum  acacia  or  glue  is  applied.  The 
vessel  is  placed  in  an  air-bath  and  heated.  The  glue  on 
hardening  generally  carries  with  it  some  of  the  outer 
coat.  The  glue  or  gum  is  then  broken  off,  dissolved  in 
water  and  the  enamel  pieces  collected  on  a  filter  paper. 
Some  obstinate  enamels  require  painstaking  methods, 
such  as  chipping  off  with  a  chisel  and  separating  the  dif- 
ferent coats — which  always  vary  somewhat  in  color — by 
picking  out  and  sorting,  using  a  pair  of  forceps.  A  large 
reading  glass  will  be  useful  in  making  these  separations. 
Any  iron  from  the  vessel  which  may  adhere  to  the  enamel 
may  be  removed  by  means  of  a  magnet  after  the  sample 
is  ground. 

Analysis  of  an  Enamel  Containing  Fluorine 

In  an  enamel  containing  fluorine  the  usual  methods 
for  silicates  cannot  be  used,  as  silicon-tetra-fluoride  would 
be  volatilized  in  the  evaporation  with  hydrochloric  acid 
for  the  separation  of  the  silica. 

Fluorine.  One  gram  sample  is  very  finely  ground, 
slowly  fused  with  two  grams  each  of  potassium  carbonate 
and  sodium  carbonate.  The  melt  should  be  kept  in  quiet 
fusion  over  as  low  a  flame  as  possible  for  one  hour.  The 
melt  is  transferred,  (after  cooling  quickly  by  giving  the 


Compte  Rendus  8,  p.  480. 

71 


crucible  a  gyratory  motion  while  held  in  the  tongs,  caus- 
ing the  melt  to  cling  to  the  sides  instead  of  forming  a 
solid  cake  in  the  bottom),  to  a  platinum  dish  where  it  is 
covered  with  a  watch  glass  and  boiled  vigorously  with 
one  hundred  cc.  of  water.  The  residue  is  filtered  off  and 
is  saved  for  the  determination  of  the  metallic  oxides  and 
the  silica. 

The  covered  solution  is  digested  on  a  steam  bath  for 
an  hour  with  several  grams  of  ammonium  carbonate,  and 
on  cooling  more  carbonate  is  added  and  the  solution  is 
allowed  to  stand  for  twelve  hours.  The  precipitate  of 
silica,  alumina,  etc.,  is  filtered  off,  washed  with  ammo- 
nium carbonate  water  and  is  saved  for  further  determi- 
nations. 

The  solution  containing  all  the  fluorine  and  traces  of 
silica,  phosphate,  etc.,  is  evaporated  until  gummy,  then 
diluted  with  water  and  neutralized  as  follows:  Phe- 
nolphthalein  is  added,  and  nitric  acid  (double  normal) 
drop  by  drop  until  solution  is  colorless. 

The  solution  is  boiled  and  the  red  color  which  reap- 
pears is  again  discharged  with  nitric  acid,  boiled  again 
and  neutralized  again  until  one  cc.  of  acid  will  discharge 
the  color. 

The  last  traces  of  silica,  etc.,  are  now  removed,  as 
recommended  by  F.  Seemann  (Zeit.  Anal.  Chem.  44,  p. 
343),  by  the  addition  of  20  cc.  of  Schaffgotsch  solution. 
This  solution  is  made  as  follows :  250  grams  of  ammonium 
carbonate  are  dissolved  in  180  cc.  of  ammonia  (0.92  sp. 
gr.)  and  the  solution  is  made  up  to  one  liter.  To  the  cold 
solution  20  grams  of  freshly  precipitated  mercuric  oxide 
are  added  and  the  solution  is  vigorously  shaken  until  the 
mercuric  oxide  is  dissolved. 

The  precipitate  caused  by  the  Schaffgotsch  solution 
is  filtered  off  and  saved,  and  the  solution  is  evaporated 
to  dryness  and  the  residue  taken  up  with  water. 

72 


Any  phosphorus  from  the  bone  ash  used  in  some 
enamels,  and  chromium  which  may  be  present,  are  re- 
moved from  this  alkaline  solution  by  adding  silver  nitrate 
in  excess.  Phosphate,  chromate  and  carbonate  of  silver 
are  here  thrown  down  and  may  be  determined  if  desired. 

The  excess  of  silver  is  removed  from  the  solution  by 
sodium  chloride,  and  one  cc.  double  normal  sodium  car- 
bonate solution  is  added  to  the  filtrate,  and  the  fluorine 
is  precipitated  by  boiling  with  a  large  excess  of  calcium- 
chloride  solution. 

The  precipitate,  consisting  of  a  mixture  of  calcium 
carbonate  and  fluoride,  is  collected  on  a  blue  ribbon  filter 
paper  and  is  washed,  dried,  ignited  at  low  red  heat,  sep- 
arated from  the  filter  paper,  and  the  residue  with  the  ash 
of  the  paper  is  treated  with  dilute  acetic  acid  until  carbon 
dioxide  is  no  longer  given  off  on  heating.  The  liquid  is 
then  evaporated  to  dryness,  the  residue  taken  up  with  hot 
water  (slightly  acidified  with  acetic  acid)  filtered,  dried 
and  gently  ignited  and  weighed  as  CaF2.  This  may  be 
checked  by  heating  with  sulfuric  acid,  driving  off  all  the 
excess  of  acid  and  reweighing  as  CaSO4.  This  method 
gives  results  for  the  amount  of  fluorine  checking  within 
0.2%,  but  which  are  generally  from  2%  to  4%  low. 

Silica.  For  the  estimation  of  silica  and  the  metallic 
oxides,  first  the  precipitate  from  the  Schaffgotsch  mer- 
curic oxide  solution  is  ignited  to  drive  off  the  mercuric 
oxide,  and  the  silica  left  is  weighed.  The  residue  from 
the  original  melt,  together  with  the  precipitate  obtained 
by  ammonium  carbonate  (after  the  drying  and  removal 
from  the  filter  paper  whose  ash  is  added)  are  then  dis- 
solved in  hydrochloric  acid.  The  solution  is  evaporated 
to  dryness  and  moistened  with  hydrochloric  acid.  It  is 
diluted  with  water  and  the  silica  is  filtered  off,  weighed, 
and  this  with  that  previously  obtained  is  the  total  silica. 

Iron,  Alumina  and  Manganese.  The  solution  from 
the  silica  is  raised  to  boiling  and  the  iron  and  aluminum 


are  precipitated  as  hydroxides.  Then  5  cc.  of  bromine 
water  is  added  and  the  boiling  continued  for  five  minutes. 
The  precipitate  is  dried  on  filter-paper  and  ignited  separ- 
ately from  it  in  a  weighed  platinum  crucible,  to  which 
the  ash  of  the  filter-paper  is  afterwards  added.  The  pre- 
cipitate consists  of  A12O3,  Fe2O3,  and  Mn2O3,  and  is 
weighed  as  such.  It  is  then  fused  with  fifteen  times  its 
weight  of  potassium  pyrosulfate  over  a  low  flame  for 
three  hours  with  the  crucible  covered.  The  crucible,  con- 
tents and  cover  are  placed  in  a  beaker  and  dilute  sulfuric 
acid  (10:1)  is  added.  By  warming  and  continued  shak- 
ing of  liquid  complete  solution  may  be  obtained.  It  is 
then  drawn  through  a  Jones  Reductor  to  change  all  the 
iron  to  ferrous  and  titrated  with  N/10  potassium  perman- 
ganate solution.  The  iron  is  calculated  to  Fe2O3  and  the 
alumina  determined  by  difference. 

If  manganese  is  present  it  is  determined  in  a  separate 
sample  in  a  method  given  later  and  is  subtracted  from  the 
iron  in  the  above.  In  white  enamels  containing  only  a 
trace  of  iron  the  manganese  may  be  determined  in  the 
solution  from  the  pyrosulfate  fusion.  A  freshly  prepared 
solution  of  potassium  ferrocyanide  is  added  to  oxidize 
the  manganese,  then  the  solution  is  made  alkaline  with 
sodium  hydroxide  solution  and  the  manganese-dioxide 
thus  formed  is  filtered  off.  The  solution  is  then  made 
acid  and  the  ferrocyanide  is  titrated  with  N/10  potassium 
permanganate  solution.  (1  cc.  KMnO4  =  0.00435  gram 
MnO.) 

Calcium  Oxide.  The  filtrate  from  the  iron  and 
alumina  is  raised  to  boiling,  treated  with  boiling  ammon- 
ium oxalate  solution  and  digested  on  water  bath  until 
precipitate  readily  and  quickly  settles  after  being  stirred. 
The  calcium  oxalate  is  now  filtered  off  and  ignited  wet  in 
platinum  to  constant  weight  over  a  strong  blast. 

Magnesium  Oxide.  The  solution  is  evaporated  to 
dryness  and  the  residue  ignited  to  remove  ammonium 
salts.  The  residue  is  treated  with  a  few  drops  of  hydro- 

74 


chloric  acid  and  taken  up  with  boiling  water  and  filtered 
from  the  carbonaceous  residue.  To  the  boiling  solution 
is  added  drop  by  drop  a  solution  of  sodium  ammonium 
phosphate  and  is  allowed  to  cool.  Half  as  much  concen- 
trated ammonium  hydroxide  is  added  as  there  is  solution 
and  it  is  allowed  to  stand  over  night.  The  precipitate  is 
collected  on  a  filter,  washed  with  3%  ammonia  water, 
dried  in  oven  and  ignited  separate  from  the  filter.  The 
heat  is  applied  gently  at  first  and  finally  with  the  highest 
heat  of  a  good  Bunsen  burner.  It  is  then  weighed  as 
Mg2P207. 

1  gram  MgsPsO  =  .3625  grams  MgO 

The  alkalies  are  determined  by  the  method  of  J. 
Lawrence  Smith  from  a  gram  sample  finely  powdered. 
This  method  is  standard  and  need  not  be  given  here. 

Separation  and  Determination  of  Antimony,  Tin, 
Manganese  and  Cobalt  in  Enamel 

Decomposition.  Two  grams  finely  powdered  sample 
are  transferred  to  a  platinum  dish,  and  after  moistening 
with  a  little  water,  pure  hydrofluoric  acid  is  added  and 
the  whole  is  mixed  with  a  platinum  spatula.  The  dish  is 
digested  on  steam  bath  for  five  hours  covered  with  plati- 
,num  cover  (a  larger  platinum  dish  may  be  used  for  cover 
if  no  other  is  at  hand).  After  the  decomposition  is  com- 
plete the  solution  is  evaporated  to  dryness  on  steam  bath. 
The  residue  is  moistened  with  enough  dilute  sulfuric  acid 
(1:1)  to  make  a  thin  paste,  and  evaporated  as  far  as 
possible  on  a  steam  bath  and  then  on  a  hot  plate,  all  the 
time  being  covered  to  prevent  spirting.  As  soon  as  fumes 
of  sulfuric  anhydride  cease  to  be  evolved  the  cover  is 
strongly  heated  until  fumes  cease  to  be  driven  off,  when 
it  is  removed.  The  contents  are  heated  by  bringing  the 
dish  to  dull  redness  directly  over  a  Bunsen  burner.  The 
sulfates  thus  formed  are  moistened  with  strong  hydro- 
chloric acid,  a  little  hot  water  is  added  and  the  solution 
boiled  with  repeated  additions  of  acid  and  water  until 

75 


completely  in  solution.  In  some  enamels — especially 
those  with  high  melting  points — the  stannic  oxide  remains 
undissolved,  and  a  fusion  of  the  residue  with  sulfur  and 
sodium  carbonate  as  given  later  under  "The  Analysis  of 
Oxide  of  Tin"  may  be  necessary. 

Treatment  with1  H2S.  The  solution  containing  at 
least  30  cc.  double  normal  hydrochloric  acid  is  transferred 
to  a  500  cc.  Ehrlenmeyer  flask  fitted  with  a  double  bored 
stopper.  Through  one  of  the  holes  a  right-angled  piece 
of  glass  tubing  is  introduced  that  just  reaches  to  the  lower 
edge  of  the  stopper,  while  through  another  hole  another 
right-angled  glass  tube  is  fixed  so  that  it  almost  reaches 
the  bottom  of  the  flask. 

A  Kipp  H2S  generator  is  connected  to  the  longer  tube 
and  H2S  is  passed  through  for  half  an  hour  and  the  solu- 
tion is  let  stand  for  another  half  an  hour,  after  which  the 
sulfides  of  antimony  and  tin  are  transferred  to  a  filter 
paper  and  the  solution  is  kept  for  the  determination  of 
manganese  and  cobalt. 

Antimony  and  Tin.  The  precipitated  sulfides  are 
dissolved  in  a  solution  of  potassium  polysulfide — if  any 
lead  or  copper  is  present  it  will  remain  undissolved  and 
may  be  determined  separately — by  pouring  this  succes- 
sively through  the  filter  into  a  300  cc.  Jena  beaker,  and 
finally  washing  with  water  containing  a  small  amount  of 
potassium  polysulfide. 

Antimony.  The  antimony  and  tin  in  this  solution 
are  separated  by  F.  W.  Clark's  method  as  modified  by 
F.  Henz1,  as  follows: 

To  the  solution  in  the  Jena  beaker  6  grams  caustic 
potash  and  3  grams  tartaric  acid  are  added.  To  this 
mixture  twice  as  much  30  per  cent,  hydrogen  peroxide  is 
added  as  is  necessary  to  completely  decolorize  the  solu- 
tion, and  the  latter  is  now  heated  to  boiling  and  kept  there 

'Treadwell,  Vol.  II,  p.  188. 

76 


until  the  evolution  of  oxygen  is  over,  in  order  to  oxidize 
the  thiosulphate  formed.  All  of  the  excess  of  peroxide 
cannot  be  removed  successfully  at  this  point.  The  solution 
is  cooled  somewhat,  the  beaker  covered  with  a  watch- 
glass,  and  a  hot  solution  of  15  grams  pure  recrystallized 
oxalic  acid  is  cautiously  added  (5  gms.  for  0.1  gm.  of  the 
mixed  metals) .  This  causes  the  evolution  of  considerable 
carbon  dioxide.  Now,  in  order  to  completely  remove  the 
excess  of  hydrogen  peroxide  the  solution  is  boiled  vigor- 
ously for  ten  minutes.  The  volume  of  the  liquid  should 
amount  to  from  80  to  100  cc.  After  this  a  rapid  stream 
of  hydrogen  sulfide  is  conducted  into  the  boiling  solution, 
and  for  some  time  there  will  be  no  precipitation,  but  only 
a  white  turbidity  formed.  At  the  end  of  five  or  ten  min- 
utes the  solution  becomes  orange  colored  and  the  anti- 
mony begins  to  precipitate,  and  from  this  point  the  time  is 
taken.  At  the  end  of  fifteen  minutes  the  solution  is  di- 
luted with  hot  water  to  a  volume  of  250  cc.,  at  the  end  of 
another  fifteen  minutes  the  flame  is  removed,  and  ten 
minutes  later  the  current  of  hydrogen  sulfide  is  stopped. 
The  precipitated  antimony  pentasulfide  is  filtered  off 
through  a  Gooch  crucible  which,  before  weighing  and 
after  drying,  has  been  heated  in  a  stream  of  carbon  di- 
oxide at  300°  C.  for  at  least  one  hour.  The  precipitate 
is  washed  twice  by  decantation  with  1  per  cent,  oxalic 
acid  and  twice  with  very  dilute  acetic  acid  before  bring- 
ing it  in  the  crucible.  Both  of  these  wash  liquids  should 
be  boiling  hot  and  saturated  with  hydrogen  sulfide. 

The  crucible  is  heated  in  a  current  of  carbon  dioxide 
(free  from  air)  to  constant  weight,  and  its  contents 
weighed  as  Sb2S3. 

The  filtrate  is  evaporated  to  a  volume  of  about  225 
cc.,  transferred  to  a  weighed  unpolished  platinum  dish, 
and  electrolyzed  at  60°  to  80°  C.  with  a  current  of  0.2  to 
0.3  ampere  (corresponding  to  2  to  3  volts).  For  very 
small  amounts  of  tin,  a  current  of  not  over  0.2  ampere 
should  be  used.  At  the  end  of  six  hours  8  cc.  of  sulfuric 

77 


acid  (1:1)  are  added,  and  at  the  end  of  twenty-four 
hours  the  solution  is  transferred  to  another  dish.  The 
deposited  tin  has  a  beautiful  appearance,  similar  to  silver. 

Tin.  The  plated  tin  is  washed  thoroughly  with  water 
and  the  dish  is  dried  in  an  air  oven  at  110°  and  weighed. 

The  solution  containing  the  cobalt  and  manganese  is 
boiled  until  free  from  H2S.  The  iron  is  oxidized  back  to 
the  ferric  state  by  the  addition  of  bromine  water  and 
boiling  until  the  excess  of  the  latter  is  expelled.  Ten  cc. 
double  normal  ammonium  chloride  is  added  and  the  iron 
and  alumina  are  precipitated  by  the  addition  of  ammonia 
and  are  filtered  off.  (The  iron  alumina  may  be  deter- 
mined from  this  precipitate  if  desired.) 

The  solution  still  containing  the  manganese  and  co- 
balt is  transferred  to  an  Ehrlenmeyer  flask  fitted  for  pass- 
ing in  H2S,  as  before  described,  and  3  cc.  strong  ammonia 
is  added.  H2S  is  passed  through  for  some  time,  and  after 
precipitation  ceases  3  cc.  more  of  ammonia  are  added  and 
the  flask  is  filled  to  the  neck  (300  cc.  flask),  is  corked  and 
set  aside  for  twelve  hours  at  least.  The  precipitate  is 
collected  and  washed  on  a  small  filter  with  water  contain- 
ing ammonium  chloride  and  sulfide. 

Manganese.  The  manganese  is  extracted  from  the 
precipitate  on  the  filter  by  pouring  through  it  strong  H2S 
water  acidified  with  1-5  its  volume  hydrochloric  acid  (sp. 
gr.  1.11) .  This  solution  from  the  extraction  is  evaporated 
to  dryness,  ammonium  salts  are  destroyed  by  evaporation 
with  a  few  drops  of  sodium  carbonate  solution,  hydro- 
chloric acid  and  a  drop  of  sulfurous  acid  are  added  to 
decompose  excess  of  carbonate  and  to  dissolve  the  pre- 
cipitated manganese,  and  the  latter  is  reprecipitated  at 
boiling  heat  by  sodium  carbonate  after  evaporating  off 
the  hydrochloric  acid.  The  manganese  is  weighed  as 
Mn3O4  and  calculated  to  MnO2,  in  which  form  it  is  prob- 
ably present  in  the  enamel. 

The  residue  of  cobalt  sulfide  left  after  extracting  the 
manganese  is  burned  in  a  porcelain  crucible,  dissolved  in 

78 


aqua  regia,  and  evaporated  with  hydrochloric  acid;  the 
platinum — and  copper  if  any  is  present — are  thrown 
down  by  heating  and  passing  in  hydrogen  sulfide.  The 
filtrate  from  the  platinum  and  copper  is  made  ammonia- 
cal,  and  cobalt  is  thrown  down  by  hydrogen  sulfide.  This 
is  filtered  off  and  washed  with  water  containing  ammo- 
nium sulfide.  This  is  either  ignited  and  weighed  as  oxide 
or  more  accurately  determined  by  dissolving  in  an  ammo- 
niacal  solution  of  ammonium  sulfate,  containing  10  grams 
of  ammonium  sulfate  and  40  cc.  of  concentrated  ammonia 
for  each  0.3  grams  of  cobalt,  and  electrolyzing  in  a 
weighed  platinum  dish  at  room  temperature  with  a  cur- 
rent of  0.5  to  1.5  ampere,  and  an  electromotive  force  of 
2.8  to  3.3  volts.  The  electrolysis  is  finished  in  three  hours. 
The  circuit  is  broken  and  the  liquid  poured  off,  and  the 
platinum  dish  is  washed  with  water,  then  with  absolute 
alcohol  (distilled  one  hour)  and  finally  with  ether,  al- 
lowed to  dry  in  oven  at  95°  for  one  minute  and  then 
weighed.  The  metallic  cobalt  is  calculated  as  CoO,  in 
which  form  it  is  present  in  the  enamel. 

The  Determination  of  Boric  Anhydride  in  Enamel 

The  boron  is  determined  in  a  separate  sample  of 
about  0.3  grams.  This  finely  pulverized  sample  is  fused 
with  three  grams  sodium  carbonate  for  fifteen  minutes, 
is  taken  up  with  thirty  cc.  dilute  hydrochloric  acid  and  a 
few  drops  of  nitric  acid.  The  melt  is  heated  in  a  250  cc. 
round-bottomed  flask  almost  to  boiling,  and  dry  precipi- 
tated calcium  carbonate  is  added  in  moderate  excess.  The 
solution  is  boiled  in  the  flask  after  it  has  been  connected 
with  a  six-inch  worm  reflux  condenser.  The  precipitate 
is  filtered  on  an  8  cm.  Buchner1  funnel,  and  is  washed 
several  times  with  hot  water,  taking  care  that  the  total 
volume  of  the  liquid  does  not  exceed  100  cc. 

The  filtrate  is  returned  to  the  flask,  a  pinch  of  cal- 
cium carbonate  is  added  and  the  solution  is  heated  to 

1  See  Method  of  Wherry  and  Chapin,  Jr.,  Am.  Chem.  Soc.  30,  p.  1688,  for  Deter- 
mination of  Boron  in  Silicates. 

79 


boiling  to  remove  the  free  carbon  dioxide.  This  is  best 
done  by  connecting  the  flask  to  a  suction  pump,  and  the 
suction  is  applied  during  boiling.  The  solution  is  cooled 
to  ordinary  temperature,  filtered  if  the  precipitate  has  a 
red  color,  and  four  or  five  drops  of  phenolphthalein  is 
added  and  N/10  sodium  hydroxide  solution  is  run  in 
slowly  until  liquid  has  a  strongly  pink  color.  A  gram  of 
mannite  (or  150  cc.  of  neutral  glycerol)  is  added,  where- 
upon the  pink  color  will  disappear.  Continue  to  run  in 
N/10  sodium  hydroxide  until  end  point  is  reached.  Add 
more  mannite  or  glycerol  and  if  necessary  more  alkali, 
until  a  permanent  pink  color  is  obtained. 

1  cc.  N/10  Sodium  Hydroxide  =  .0035  g.  BaO« 

Lead.  The  enamel  for  cooking  utensils  should  never 
contain  lead.  To  determine  whether  a  cooking  utensil 
contains  lead,  E.  Adam  gives  the  following  simple  quali- 
tative method:  A  small  piece  of  filter  paper  moistened 
with  hydrofluoric  acid  is  placed  upon  the  enamel  and  al- 
lowed to  remain  for  some  minutes;  the  paper,  together 
with  any  pasty  mass  adhering  to  the  enamel,  is  then 
washed  off  into  a  small  platinum  basin,  diluted  with 
water,  and  tested  for  lead  by  passing  H2S  through  the 
solution. 

J.  Grunwald  (Oesterr.  Chem.  Ztg.  8,  p.  46)  gives  an- 
other quick  test  for  lead :  Wet  small  portion  of  surface 
with  HNO3  (cone.)  and  heat  until  acid  is  evaporated. 
Add  several  drops  of  water  and  a  few  drops  10  %  potas- 
sium iodide  solution,  and  if  even  a  trace  of  lead  is  present 
yellow  lead-iodide  will  be  produced. 

Determination  of  Phosphoric  Anhydride  in  Enamel 

Enamels  containing  bone  ash  to  give  opaqueness  are 
analyzed  for  P2O5  as  follows: 

To  a  gram  sample  of  very  finely  pulverized  enamel 
in  a  platinum  crucible  one  cc.  of  sulfuric  acid  is  added 
and  the  crucible  is  filled  half  full  (about  ten  cc.  are  re- 

80 


quired)  with  hydrofluoric  acid.  The  crucible  is  heated 
on  the  water  bath  until  most  of  the  solution  is  evaporated 
and  then  gently  on  a  hot  plate  to  remove  all  the  fluorine 
as  silicon-tetra-fluoride  and  as  hydrofluoric  acid,  but  no 
sulfuric  acid  fumes  should  evolve,  as  P2O5  is  volatile.  The 
residue  is  dissolved  in  nitric  acid  and  taken  to  dryness, 
moistened  with  nitric  acid,  diluted  with  water,  filtered 
and  washed  with  a  very  little  water. 

Add  aqueous  ammonia  to  the  solution  from  above 
until  the  precipitate  of  calcium  phosphate  first  produced 
just  fails  to  redissolve,  and  then  dissolve  this  by  adding  a 
few  drops  of  nitric  acid.  Warm  the  solution  to  about 
70°  C.  and  add  50  cc.  ammonium  molybdate  solution  (70g. 
MoO3  per  liter).  Allow  the  mixture  to  digest  at  50°  for 
twelve  hours.  Filter  off  precipitate  washing  by  decanta- 
tion  with  a  solution  of  ammonium  nitrate  made  acid  with 
nitric  acid. 

The  precipitate  on  the  filter  is  dissolved  by  pouring 
through  it  dilute  ammonia  solution  (one  volume  of  0.96 
sp.  gr.  ammonia  to  three  volumes  of  water) . 

The  solution  is  received  in  the  beaker  containing  the 
bulk  of  the  precipitate,  all  of  which  is  dissolved  in  the 
ammonia  solution. 

An  excess  of  magnesium  ammonium  chloride  ("mag- 
nesia mixture")  solution  is  added  very  slowly  and  with 
constant  stirring.  Let  solution  stand  over  night.  Decant 
clear  solution  through  a  filter  and  wash  by  decantation 
with  ammonia  water  (1:  3).  Dissolve  the  precipitate  by 
pouring  a  little  hydrochloric  acid  (sp.  gr.  1.12)  through 
the  filter,  allowing  the  acid  solution  to  run  into  the  beaker 
containing  most  of  the  precipitate.  When  all  the  precipi- 
tate on  the  filter  and  in  the  beaker  is  dissolved  wash  the 
filter  paper  with  a  little  hot  water.  To  the  solution  add 
2  cc.  magnesia  mixture  and  then  strong  ammonia,  drop  by 
drop,  with  constant  stirring  until  distinctly  ammoniacal. 
Stir  several  minutes,  then  add  strong  ammonia  equal  to 
one-third  of  the  liquid,  let  stand  two  hours  and  filter  off 

81 


the  precipitate  of  magnesium  ammonium  phosphate. 
Wash  with  dilute  ammonia  water,  dry  the  precipitate, 
ignite  separately  from  the  filter,  first  at  low  temperature 
and  gradually  raise  to  full  blast.  Weigh  precipitate  as 
Mg2P2O7  and  calculate  as  P2O5  in  sample. 


PART  II. 

THE  ANALYSIS  OF  ENAMEL  RAW  MATERIALS 
The  Analysis  of  Borax 

Sampling.  A  handful  is  taken  from  the  middle  of 
every  tenth  bag  as  it  is  unloaded.  The  sample  from  the 
entire  car-load  is  then  quartered  down  to  two  pounds. 
This  is  crushed  so  that  it  will  pass  through  a  forty  mesh 
sieve.  This  is  futher  quartered  to  about  thirty  grams. 
Sample  is  then  accurately  weighed  and  thoroughly  dis- 
solved in  about  600  cc.  hot — not  boiling — water  in  a  liter 
volumetric  flask,  and  when  cool  is  diluted  to  the  mark. 
One  hundred  cc.  of  this,  representing  one-tenth  of  the 
sample,  is  then  taken  for  analysis. 

Determination  of  Sodium  Oxide  and  Boric  Acid.  Ti- 
trate with  normal  sulfuric  or  hydrochloric  acid  solution, 
using  methyl  orange  as  indicator. 

Number  cubic  centimeters  Normal  Acid  X  .031  =  g, 
Na2O.  The  solution  is  now  boiled,  covered  with  a  watch 
glass  to  expel  CO2,  and  on  cooling  may  turn  pink.  Add 
normal  KOH  solution  (a  drop  will  do)  to  bring  back  yel- 
low color.  At  this  stage  all  the  boric  acid  exists  in  a  free 
state. 
(2Na*+B4<> )  +  HsO-h  (2Hf+2Cl-)  =  (2Na+-f  2C1-)  +4  (H*-f  4BCV) 

Add  as  much  neutral  glycerol  as  there  is  solution 
(about  150  cc.)  and  titrate  with  normal  potassium  hy- 
droxide, using  phenolphthalein  as  indicator.  If  end  is 
not  distinct  add  more  glycerol  and  more  indicator.  The 
addition  of  glycerol  causes  the  boric  acid  to  become  more 

82 


dissociated,  probably  due  to  the  formation  of  boroglyceric 
acid,  and  the  end-point  is  quite  distinct.  The  following 
equation  represents  essentially  what  takes  place: 

(4H*+4BO«-)  +  (4Kf-f  4OH-)  =  (4K*+4BO*-)  +  4H2Q 
1  cc.  normal  KOH  solution  —  .035  g.  BaO« 

If  the  analysis  gives  more  Na2O  than  is  required  to 
calculate  all  the  B2O3  to  Na2B4O7,  the  remainder  comes 
from  sodium  carbonate  with  which  it  has  been  adulte- 
rated. 

Calculation  of  Results.  The  analysis  of  the  borax  is 
very  important,  as  many  times  samples  are  adulterated, 
and  even  when  not  adulterated  seldom  contain  exactly 
enough  water  to  give  the  formula  Na2B4O7-  10H2O.  It  is 
necessary  to  know  the  strength  of  the  borax  not  only  to 
buy  intelligently,  but  also  so  that  each  and  every  mix  of 
enamel  will  contain  the  same  amount  of  borax. 

It  is  customary  to  calculate  from  the  percent  of  B2O3 
in  sample  the  percent  strength  of  the  sample  as  Na2 
B4O710H2O. 

X  2.7307  =  %Na*B*O 


When  the  sample  has  dehydrated  of  course  this  will 
run  over  100%,  and  thus  the  correspondingly  fewer 
pounds  of  borax  may  be  used  in  the  mix  of  enamel. 

Moisture.  On  account  of  the  large  amount  of  water 
of  crystallization  in  borax  it  is  difficult  to  determine  the 
moisture  directly,  therefore  it  is  calculated  by  subtracting 
the  %  Na2B4O7  10H2O  and  the  %  Na2CO8  (if  any  is 
present)  from  100%. 

The  Analysis  of  Ground  Sand,  Flint  and  Quartz 

Fineness.  These,  as  are  most  of  the  raw  materials 
used  in  the  enamel,  are  tested  for  fineness.  One  kilogram 
is  weighed  on  balance  sensitive  to  1/10  gram  and  is 
shaken  on  a  100  mesh  sieve.  The  material  remaining  on 


the  sieve  is  weighed.  This  is  then  shaken  on  an  80  mesh 
sieve  and  the  residue  weighed.  From  this  is  calculated 
percent  through  100  mesh  and  percent  through  80  mesh. 
The  finer  the  material  the  better  it  is  for  use  in  making 
enamel. 

An  analysis  for  SiO2,  Fe2O3  and  MgO  is  run  when  a 
new  material  is  being  tried,  but  generally  only  the  SiO2 
and  Fe2O3  are  determined.  In  this  case  the  acid  solution 
from  the  silica  is  reduced  by  passing  through  a  Jones 
Reductor  and  is  titrated  with  N/10  potassium  bichromate. 

Preparation  for  Analysis.  The  material  is  carefully 
sampled  by  quartering  down  to  several  grams.  This  is 
ground  in  an  agate  mortar  to  pass  completely  through  a 
hundred  mesh  sieve.  This  grinding  is  generally  done  by 
hand  but  an  enameling  works  laboratory  should  be 
equipped  with  a  McKenna  Grinder,  (manufactured  by 
McKenna  Bros.  Brass  Company,  Ltd.,  of  Pittsburgh),  in 
which  the  material  can  be  ground  in  an  agate  mortar  by 
power. 

The  method  followed  for  the  analysis  of  flint  and 
other  forms  of  silica  as  well  as  clays  and  feldspars,  is  in 
all  essentials,  a  well  known  method  given  by  Hillebrand 
in  analysis  of  silicate  rocks,  U.  S.  Geological  Survey  Bull. 
305,  and  for  reasons  of  space  this  method  will  not  be 
given  here. 

The  Determination  of  Titanium  in  Enamels,  Clays  and 
Silicate  Minerals 

Titanium  is  determined  after  the  determination  of 
the  iron  by  titrating  with  permanganate.  This  solution 
(after  titrating)  is  diluted  to  1000  cc.  and  is  treated  with 
hydrogen  peroxide  and  the  titanium  determined  by  A. 
Weller's  Colorimetric  Method,1  from  one-half  the  solution. 

This  determination  depends  upon  the  fact  that  acid 
solutions  of  titanium  sulphate  are  colored  intensely  yel- 


1  Berichte  15.  p.  25-98. 

84 


low  when  treated  with  hydrogen  peroxide;  the  yellow 
color  increases  with  the  amount  of  titanium  present  and 
is  not  altered  by  an  excess  of  hydrogen  peroxide.  On  the 
other  hand,  inaccurate  results  are  obtained  in  the  pres- 
ence of  hydro-fluoric  acid  (Hillebrand)  ;  consequently  it 
is  not  permissible  to  use  hydrogen  peroxide  for  this  de- 
termination which  has  been  prepared  from  barium  per- 
oxide by  means  of  hydrofluosilicic  acid.  Furthermore, 
chromic,  vanadic,  and  molybdic  acids  must  not  be  present, 
since  they  also  give  colorations  with  hydrogen  peroxide. 
The  presence  of  small  amounts  of  iron  do  not  affect  the 
reaction,  but  large  amounts  of  iron  cause  trouble  on  ac- 
count of  the  color  of  the  iron  solution.  If,  however,  phos- 
phoric acid  is  added  to  the  colored  ferric  solution  it  be- 
comes decolorized,  and  from  such  a  solution  the  determi- 
nation of  titanium  offers  no  difficulty.  The  solution  in 
which  the  titanium  is  to  be  determined  must  contain  at 
least  5  per  cent,  of  sulfuric  acid;  an  excess  does  not  in- 
fluence the  reaction.  The  reaction  is  so  delicate  that 
0.00005  gm.  of  TiO2  present  as  sulphate  in  50  cc.  of  solu- 
tion give  a  distinctly  visible  yellow  coloration. 

For  this  determination  a  standard  solution  of  titan- 
ium sulfate  is  required.  This  can  be  prepared  by  taking 
0.6000  gm.  of  potassium  titanic  fluoride  which  has  been 
several  times  recrystallized  and  gently  ignited  (corres- 
ponding to  0.2  gm.  of  TiO2).  This  is  treated  in  a  platinum 
crucible  several  times  with  a  little  water  and  concentrated 
sulfuric  acid,  expelling  the  excess  of  acid  by  gentle  igni- 
tion, finally  dissolving  in  a  little  concentrated  sulfuric 
acid  and  diluting  with  5  per  cent,  sulfuric  acid  to  100  cc. 
One  cubic  centimeter  of  this  solution  corresponds  to  0.002 
gm.  TiO2. 

The  determination  proper  is  carried  out  in  the  same 
way  as  the  colorimetric  determination  of  ammonium  in 
the  sanitary  analysis  of  water. 

50  cc.  of  the  solution  which  has  been  brought  to  a 
definite  and  accurately  measured  volume  is  placed  in  a 

85 


Nessler  tube  beside  a  series  of  other  tubes,  each  contain- 
ing a  known  amount  of  the  standard  titanium  solution, 
filled  up  to  the  mark  with  water  and  each  treated  with 

2  cc.  of  3  per  cent,  hydrogen  peroxide1  (free  from  hydro- 
fluoric acid).     The  color  of  the  solution  in  question  is 
compared  with  the  standards.    This  method  is  only  suit- 
able for  the  estimation  of  small  amounts  of  titanium,  as 
the  shades  of  strongly  colored  solutions  cannot  be  com- 
pared accurately. 

The  Analysis  of  Oxide  of  Tin 

Stannic  Oxide.  As  this  is  one  of  the  most  important 
and  most  expensive  of  the  raw  materials  used  in  enamel- 
ing, an  analysis  is  very  necessary.  The  oxide  is  bought 
to  contain  not  less  than  99.5%  SnO2,  and  in  this  the  im- 
purities will  consist  of  minute  traces  only  of  other  ma- 
terials. For  an  oxide  of  this  kind  from  .2  to  .3  of  a  gram 
of  the  sample  is  placed  in  a  porcelain  casserole,  about 
10  cc.  of  C.  P.  nitric  acid  of  a  sp.  gr.  1.2  is  added  and  the 
solution  is  slowly  evaporated  to  a  volume  of  about  2  or 

3  cc.,  diluted  to  about  30  or  40  cc.  of  water,  kept  warm 
for  about  a  half  hour,  filtered  on  a  small  blue-ribbon  filter 
paper,  and  washed  with  warm  water,  slightly  acidulated 
with  nitric  acid,  being  careful  to  avoid  letting  the  preci- 
pitate creep  up. 

The  precipitate  is  dried  on  filter  paper  in  the  funnel 
by  placing  in  a  hot  air  bath.  The  dried  tin  oxide  is  then 
removed  as  completely  as  possible  from  the  filter  paper 
and  the  paper  is  ignited  in  a  porcelain  crucible,  being 
sure  that  there  is  an  excess  of  air  so  that  there  will  be  no 
metallic  tin  reduced. 

The  balance  of  oxide  of  tin  is  now  added  to  the  cru- 
cible and  the  whole  is  moistened  with  a  drop  of  nitric 
acid,  the  temperature  under  the  crucible  is  gradually 
raised  until  it  comes  to  a  bright  red  heat  over  the  blast 
flame. 


1The  hydrogen   peroxide  solution  is   prepared  shortly  before  using  by  dissolving 
commercial   potassium  percarbonate  in  dilute  sulfuric  acid. 

86 


This  method  gives  results  which  check  within  one- 
tenth  of  a  per  cent. 

Some  brands  of  oxide  of  tin  on  the  market  contain  a 
number  of  impurities  in  considerable  quantities.  Lead, 
iron,  silica,  Sodium  chloride,  sodium  sulfate  and  water 
are  the  most  common  of  these.  These  are  determined  as 
follows : 

Direct  Method.  Methods  for  the  direct  determina- 
tion of  the  tin  have  proven  quite  unsatisfactory  b.ut  the 
following,  with  very  careful  manipulation,  yields  results 
checking  within  0.2%: 

Five-tenths  grams  of  oxide  is  mixed  in  a  porcelain 
crucible  with  3  grams  each  of  powdered  sulfur  and  dry 
carbonate  of  soda,  which  both  of  course  must  be  C.  P., 
especially  free  of  metals  and  earths.  The  covered  cruci- 
ble is  heated  for  about  an  hour  at  low  heat  first,  and  later 
at  the  heat  of  a  regular  Bunsen  burner ;  then  let  cool  with- 
out lifting  the  cover.  The  cold  mass  is  dissolved  in  water, 
filtered  and  washed  with  water  to  which  was  added  a 
little  sulfide  of  ammonia;  the  residue  is  brought  back  in 
the  crucible  and  the  melting  process  repeated,  of  which 
the  solution  is  filtered  to  the  first  melting.  The  sulfide  tin 
solution  then  is  acidulated  with  hydrochloric  acid  and  the 
precipitated  sulfide  of  tin  is  allowed  to  settle  clearly,  after 
which  it  is  filtered  and  washed  with  sulfide  of  hydrogen 
water. 

The  wet  precipitate  of  sulfide  of  tin  is  transferred 
to  an  Ehrlenmeyer  flask  and  treated  with  dilute  hydro- 
chloric acid  and  bromine  until  completely  dissolved,  at  a 
low  heat.  The  filter  left  after  the  solution  is  filtered  off 
is  washed  and  the  SnCl2  solution  is  precipitated  with  am- 
monia and  a  little  nitrate  of  ammonia,  allowed  to  settle, 
filtered  and  washed.  After  drying^  the  precipitate  is 
ignited  at  white  heat  and  is  weighed  as  SnO2. 

Reduction  Method.  When  the  qualitative  analysis 
shows  no  metal  other  than  tin  present,  a  very  satisfactory 

87 


method  is  to  reduce  a  weighed  quantity  of  the  sample  in 
a  Rose  crucible  by  heating  to  redness  in  a  stream  of  hy- 
drogen. The  silica,  if  any  is  present,  may  be  determined 
by  dissolving  out  the  tin  with  hydrochloric  acid  and 
weighing  the  residue. 

Combined  Water.  In  oxides  which  are  prepared  by 
certain  precipitation  methods,  the  combined  water  runs 
as  high  as  ten  per  cent.  To  determine  this,  a  two  gram 
sample  is  heated  in  a  porcelain  crucible  at  a  white  heat 
to  constant  weight.  The  loss  is  combined  water. 

Lead.  The  lead  is  determined  from  the  nitric  acid 
solution  and  washings  from  the  tin  oxide  determination 
by  precipitation  as  the  sulfate. 

Iron.  Digest  about  one  gram  with  twenty-five  cc. 
of  concentrated  hydrochloric  acid.  As  much  water  is 
added  and  the  solution  is  boiled  for  five  minutes.  The 
residue  is  filtered  off  and  about  a  cubic  centimeter  of  con- 
centrated sulfuric  acid  is  added  and  the  solution  is  evap- 
orated until  the  sulfuric  fumes  come  off.  The  solution  is 
diluted,  passed  through  a  Jones  Reductor  and  titrated 
with  N/10  potassium  permanganate  solution. 

Soluble  Salts.  About  two  grams  of  the  sample  is 
boiled  with  water  for  thirty  minutes.  The  residue  is  fil- 
tered on  a  blue-ribbon  paper  and  is  dried  in  an  air  bath. 
It  is  then  separated  as  completely  from  the  paper  as  is 
possible.  The  paper  is  burned  in  a  platinum  crucible.  A 
drop  of  nitric  acid  is  added  and  the  crucible  is  raised  to 
bright  red.  The  whole  of  the  residue  is  now  added  and 
heated  to  white  heat  for  some  time.  (If  there  was  com- 
bined water  present  in  the  sample  of  course  it  will  be 
driven  off,  and  this  must  be  taken  into  calculation). 

The  loss  in  weight  (minus  the  above  correction)  is 
the  soluble  salts — usually  sodium  chloride  and  sulfate. 

If  desired  these  may  be  determined  definitely  by 
usual  methods.  (Titration  of  an  aliquot  part  with  N/10 
silver  nitrate  solution  for  the  chloride  and  precipitation  of 

88 


the  sulfate   as  barium  sulfate  in  another  aliquot  part 
slightly  acidifies  with  nitric  acid.) 

Silica.  To  the  residue  in  the  platinum  crucible  from 
the  above  determination  several  drops  of  sulfuric  acid  are 
added,  and  the  crucible  is  filled  within  a  quarter  of  an 
inch  of  the  rim  with  pure  hydrofluoric  acid.  This  is 
volatilized,  carrying  with  it  any  of  the  silica  as  hydrofluo- 
silicic  acid.  Loss  of  weight  =  SiO2. 

The  Analysis  of  Pyrolusite 

Pyrolusite  has  two  uses  in  enamel,  first  as  an  oxidiz- 
ing agent,  and  second  to  give  an  amethyst  color  to  the 
enamel  frit.  Its  grading,  however,  is  generally  made  on 
its  oxidizing  value.  This  is  found  as  follows : 

Manganese  Dioxide.  A  sample  is  carefully  taken 
from  each  barrel  of  the  shipment,  and  after  quartering 
down  to  about  ten  grams  is  ground  so  as  to  pass  through 
a  200  mesh  sieve.  (It  is  better  to  test  this  by  seeing  if 
any  grit  can  be  detected  when  the  powder  is  placed  be- 
tween the  teeth.)  The  sample  is  dried,  spread  out  on  a 
watch  glass,  at  110°  for  one  hour,  transferred  to  a  stop- 
pered weighing  tube,  and  after  weighing,  about  one-half 
gram  is  transferred  into  a  250  cc.  Ehrlenmeyer  flask.  For 
each  gram  of  sample  weighed  out  add  at  least  0.9  grams 
pure,  tested  oxalic  acid  (H2C2O4  2H2O)  weighing  the  acid 
accurately  and  recording  the  same.  Add  about  30  cc.  of 
water  and  30  cc.  5  normal  sulfuric  acid  and  drive  off  car- 
bon dioxide  by  heating  gently. 

It  is  seldom  necessary  to  filter  after  some  practice,  so 
the  solution  is  titrated  hot  for  the  excess  of  oxalic  acid 
with  N/10  potassium  permanganate  solution.  Calculate 
amount  of  oxalic  acid  oxidized  by  the  pyrolusite.  The 
reaction  is 

.      MnOa  +  H«CaO*  •  2H2Q  +  IfcSO*  =  MnSO*  +  2COt  -f  4H»O 

Each  gram  oxalic  acid  oxidized  therefore  corre- 
sponds to  .6902  g.  MnO2. 


As  pyrolusite  is  added  to  some  enamels  only  to  give 
color  it  is  sometimes  necessary  to  know  its  coloring  power, 
and  this  is  dependent  upon  the  total  manganese. 

Total  Manganese.  One-half  gram  sample  is  boiled 
with  strong  hydrochloric  acid  until  chlorine  ceases  to  be 
evolved.  The  solution  is  neutralized  with  calcium  carbon- 
ate and  an  excess  of  a  strong  filtered  solution  of  bleaching 
powder  is  added.  The  solution  is  boiled  until  deep  red, 
then  alcohol  is  added  until  the  red  color  disappears.  The 
whole  of  the  manganese  now  exists  as  MnO2  and  may  be 
reduced  with  oxalic  acid  and  titrated  for  its  oxidizing 
power  as  before  with  N/10  permanganate  of  potassium. 
Each  gram  of  oxalic  acid  oxidized  corresponds  to  .4361  g. 
Mn. 

The  Analysis  of  Soda  Ash  and  Pearl  Ash 

Generally  it  is  only  necessary  to  determine  the  total 
alkali  in  a  sample  of  either  soda  ash  or  pearl  ash,  and  to 
calculate  from  this  the  percentage  of  Na2O  or  K2O.  A 
more  complete  analysis  includes  the  determination  of  in- 
soluble matter,  iron,  chloride,  sulfate  and  moisture,  as 
well  as  the  total  alkali. 

Insoluble  Matter.  50  g.  weighed  on  rough  balance 
(sensitive  to  0.1  g.)  and  sufficient  water  added  to  dissolve 
the  ash,  shaking  until  dissolved.  After  an  hour's  digestion 
the  solution  is  filtered  through  a  weighed  Gooch  crucible 
with  a  circle  of  filter  paper  covering  the  bottom.  This  is 
dried  at  105°  and  the  increase  in  weight  is  insoluble 
matter. 

Iron.  The  iron  in  the  above  insoluble  matter  is  dis- 
solved by  pouring  hot  dilute  hydrochloric  acid  through 
the  precipitate  in  the  Gooch  crucible.  The  iron  is  precipi- 
tated from  this  by  ammonium  hydroxide  and  filtered  on  a 
white  ribbon  filter  paper.  The  still  moist  precipitate  is 
dissolved  in  sulfuric  acid,  reduced  by  means  of  a  Jones 
Reductor  and  titrated  with  N/10  permanganate. 

90 


Chloride.  Three  gram  samples  are  dissolved  in 
water  and  nitric  acid  added  until  the  solution  is  neutral 
(test  with  litmus  paper).  It  is  then  titrated  with  N/10 
silver  nitrate  solution. 

Sulfate.  Five  or  ten  grams  are  dissolved  in  hydro- 
chloric acid  and  the  sulfate  precipitated  from  the  almost 
boiling  solution  by  the  addition  of  hot  barium  chloride 
solution. 

Total  Alkali.  Twenty-five  grams  are  dissolved  in 
water  in  a  500  cc.  volumetric  flask  and  50  cc.  are  titrated 
with  N.  hydrochloric  acid,  using  methyl  orange  as  indi- 
cator. 

Hydroxide.  To  50  cc.  from  above,  precipitate  all  the 
carbonate  with  barium  chloride.  Without  filtering,  add 
phenolphthalein  and  titrate  until  colorless  with  normal 
hydrochloric  acid. 

Moisture.  Ten  gram  samples  are  dried  at  120°  for 
two  hours. 

The  Analysis  of  Saltpeter  and  Chili  Saltpeter 

Moisture.  Ten  gram  samples  are  heated  to  constant 
weight  in  an  air-bath  at  130°. 

Insoluble  Matter.  Twenty  grams  are  dissolved  in 
boiling  water  and  filtered  through  a  weighed  Gooch  cru- 
cible with  a  circle  of  filter  paper  on  the  bottom.  After 
drying  at  110°  in  air  bath  to  constant  weight,  the  increase 
in  weight  is  the  insoluble  matter. 

Chlorine.  The  solution  from  above — this  should  be 
about  500  cc. — is  placed  in  a  1000  cc.  volumetric  flask  and 
25  cc.  (representing  0.5  g.  sample)  is  titrated  with  N/10 
silver  nitrate,  using  potassium  chromate  as  indicator.  The 
result  is  calculated  to  sodium  chloride. 

Sulfate.  Twenty  cc.  are  heated  to  boiling  and  precip- 
itated by  adding  hot  barium  chloride  solution,  a  drop  at 

91 


a  time  and  with  constant  stirring.  After  two  hours  diges- 
tion (  or  until  precipitate  settles  quickly  after  agitating), 
filter  through  a  Gooch  crucible  with  ignited  asbestos  filter, 
ignite  and  weigh  as  barium  sulfate.  This  is  calculated  to 
calcium  sulfate. 

Calcium  and  Magnesium.  From  five  hundred  ccT~of 
the  above  solution  (equal  to  10  grams  sample)  at  boiling 
temperature  precipitate  the  calcium  as  oxalate  by  the  ad- 
dition of  ammonium  oxalate,  being  careful  not  to  add 
much  excess,  as  magnesium  is  to  be  determined  in  the 
same  sample.  Filter  on  a  white  ribbon  filter  paper,  after 
an  hour's  digestion  on  the  steam  bath,  ignite  wet  paper  in 
platinum  crucible,  gradually  increase  to  full  blast  and 
heat  to  white  heat  to  constant  weight.  Weight  as  calcium 
oxide. 

Determine  the  magnesium  in  filtrate  from  the  calcium 
by  addition  of  a  solution  of  microcosmic  salt  and  after- 
ward one-third  the  volume  of  concentrated  ammonium 
hydroxide,  added  drop  by  drop.  The  precipitate,  ignited 
separate  from  the  filter  paper,  is  heated  at  first  gently 
and  at  last  with  the  full  heat  of  a  Bunsen  burner,  and 
weighed  as  magnesium  pyrophosphate  (Mg2P2O7). 

Perchlorate.  Ten  grams  of  the  sample  of  which  the 
chloride  content  has  already  been  determined,  is  mixed 
with  an  equal  quantity  of  chemically  pure  sodium  carbon- 
ate, and  is  heated  in  a  large,  covered  platinum  crucible  to 
quiet  fusion.  Ten  or  fifteen  minutes  are  required.  The 
product  is  then  dissolved  in  nitric  acid  and  the  chloride 
estimated  as  usual. 

Nitrogen.  This  is  determined  by  the  Kjeldahl 
method  after  reducing  the  nitrate  to  ammonia.  Twenty 
grams  of  the  sample  are  ground  coarsely  and  dissolved  in 
water  in  a  liter  flask,  and  solution  is  diluted  to  the  mark. 
Twenty-five  cc.  (equal  to  0.5  g.  sample)  of  this  solution  is 
mixed  in  a  800  cc.  Kjeldahl  flask  with  15  cc.  concentrated 


sulfuric  acid  to  which  2  grams  salicylic  acid  have  been 
added,  then  add  gradually  2  grams  zinc  dust  and  shake 
flask  to  mix  contents.  Digest  over  low  flame  with  neck  of 
flask  slightly  inclined  until  danger  of  frothing  has  passed. 
Increase  flame  until  the  acid  boils  briskly  and  until  white 
fumes  cease  to  come  off.  This  usually  takes  about  ten 
minutes. 

Add  .7  gram  mercuric  oxide  and  continue  boiling, 
adding  acid  if  necessary  to  keep  solution  from  solidifying. 
Solution  should  be  clear  in  a  short  time.  Complete  oxida- 
tion by  adding  a  little  powdered  potassium  permanganate 
and  allow  the  contents  to  cool.  Add  about  200  cc.  am- 
monia-free water  and  25  cc.  potassium  sulfide  solution 
(40  g.  commercial  salt  to  the  liter)  and  shake  thoroughly. 
Add  several  pieces  of  granulated  zinc  and  then  pour  care- 
fully down  the  side  of  the  neck  100  cc.  sodium  hydroxide 
solution  (500  g.  per  liter),  avoiding  shaking  and  thereby 
mixing  the  acid  and  alkali.  After  washing  the  neck  with 
ammonia-free  water  connect  the  flask  immediately  with  a 
previously  set  up  block  tin  condenser,  which  has  been 
thoroughly  washed  and  the  tips  of  whose  delivery  are  im- 
mersed in  30  cc.  standard  acid  solution  (half  normal), 
colored  with  methyl  orange  contained  in  a  150  cc.  Phillip's 
flask.  Mix  contents  of  digestion  flask  by  shaking  thor- 
oughly, then  heat  carefully,  then  slowly  (taking  about  an 
hour)  distill  over  200  cc.  of  the  liquid.  Titrate  excess  of 
acid  with  standard  half  normal  alkali  solution,  and  from 
this  calculate  percentage  of  nitrogen  in  sample. 

Lung  Nitrometer  Method.  Where  frequent  analyses 
are  made  the  Lung1  Nitrometer  method  is  better.  A  nitro- 
meter modified  especially  for  the  use  of  the  determination 
of  nitrate  in  saltpeter  is  here  illustrated.  The  Nitrometer 
"A"  and  the  leveling  tube  "B"  are  filled  with  mercury. 
From  a  twenty  gram  sample  which  has  been  dried  at  110° 
to  constant  weight  as  nearly  as  is  possible  0.35  grams  is 
put  into  a  weighing  tube.  This  is  then  accurately  weighed 


Berichte  1886,  18,  1891. 


and  the  contents  shaken  into  the  entry  tube  "C."  The 
weighing  tube  is  again  weighed  and  the  difference  in 
weight  is  the  grams  sample  employed.  This  should  be 
close  to  0.35  grams  so  that  the  gas  evolved  will  be  more 
than  100  cc.  and  less  than  130  cc.  at  ordinary  tempera- 
ture and  pressure. 

About  .5  cc.  water  is  then  poured  in  and  the  solution 
and  crystals  (after  a  minute's  standing)  are  drawn  into 
the  measuring  tube  by  opening  the  three-way  cock  into 
the  entry  tube  "C"  and  lowering  the  leveling  bulb  cau- 
tiously. The  cup  is  washed,  using  less  than  1  cc.  of  water, 
and  about  15  cc.  of  strong  sulfuric  acid  is  admitted 
through  the  entry  tube  into  the  measuring  tube.  (More 
than  1%  cc.  H2O  renders  the  acid  too  dilute  and  the 
mercury  is  attacked) .  After  the  cock  is  closed  the  leveling 
tube  is  placed  in  a  clamp,  the  measuring  tube  is  thor- 
oughly shaken  and  the  following  reaction  takes  place : 

MnOH-H.C.0*  :  2H20+H*SO*=MnS<>f2COH-4HaO 

The  measuring  tube  is  now  placed  in  clamp  on  a  level 
with  the  levelling  tube  and  solution  is  allowed  to  cool 
for  an  hour. 

The  tube  is  then  accurately  leveled,  allowing  one 
division  of  mercury  for  each  six  and  one-half  divisions  of 
acid,  and  the  gas  volume  read  off .  The  temperature  and 
barometric  pressure  are  read  and  the  gas  corrected  to 
standard  conditions.  Each  cc.  NO  gas  corresponds  to 
.0037986  g.  NaNO3  or  .003845  g.  KNO3. 

The  Analysis  of  Cryolite 

Cryolite  is  a  mineral  occurring  in  large  quantities  in 
Greenland,  and  is  the  sodium  salt  of  hydrofluo-aluminic 
acid,  Na3AlF6.  It  is  used  in  enamels  and  is  fused,  finely 
ground  with  the  frit  giving  it  a  milky  opaqueness  which 
enamellers  call  "body."  It  is  a  very  expensive  material 
and  is  most  always  far  from  pure,  either  being  deliber- 
ately adulterated  or  merely  naturally  impure. 

94 


Methods  used  by  most  chemists  for  its  analysis  are 
at  the  best  crude.  The  direct  determination  of  the  fluorine 
is  the  only  satisfactory  means  of  properly  grading  it.  The 
method  used  for  cryolite  is  exactly  the  same  as  that  em- 
ployed in  the  analysis  of  fluorine-bearing  enamel  as  given 
in  the  beginning  of  this  article,  except  that  one  gram  of 
the  cryolite  is  finely  ground  with  about  three  grams  (ac- 
curately weighed)  of  pure  silica,  and  this  mixture  is  fused 
with  about  eight  grams  of  equal  parts  of  sodium  carbon- 
ate and  potassium  carbonate.  In  determining  the  silica 
in  the  cryolite,  this  silica  which  has  been  added  must  be 
deducted  from  that  found. 

The  alkalies  are  determined  by  the  method  of  J.  Law- 
rence Smith1  from  a  gram  sample  finely  powdered. 

Combination  of  Results.  All  soda  is  combined  with 
sufficient  fluorine  to  form  sodium  fluoride  (NaF2).  The 
remainder  of  the  fluorine  is  combined  with  aluminum  as 
aluminum  fluoride  (A1F3).  The  remainder  of  the  alumi- 
num is  calculated  as  alumina  (A12O3). 

The  Analysis  of  Fluorspar 

Fluorspar  is  analyzed  especially  for  the  fluorine  con- 
tent by  the  same  method  as  that  given  under  Cryolite.  It 
is  a  material  seldom  adulterated  and  a  mere  fusion  with 
six  times  the  weight  of  sodium  carbonate,  the  taking  to 
dryness  with  hydrochloric  acid  as  in  ordinary  silicate 
analysis,  the  removal  of  iron  and  alumina  as  hydroxide 
with  ammonia,  and  the  precipitation  with  ammonium 
oxalate  of  the  calcium  and  its  final  weighing  as  calcium 
oxide,  is  sufficient  in  most  cases.  All  the  calcium  may  be 
calculated  as  CaF2.  The  determination  of  the  fluorine, 
however,  is  of  course  the  only  exact  method  of  accurately 
grading  this  material. 

The  approximate  method  for  determining  the  fluorine 
is  as  follows: 

Approximate  Method  for  Fluorine.  About  one  gram 
of  sample  finely  ground  and  accurately  weighed  is  in- 

1  Am.  Jour.  Science  (2)  50,  p.  269.     Treadwell-Hall  Anal.  Chem.,  Vol.  II,  p.  394. 

95 


timately  mixed  in  agate  mortar  with  about  the  same  quan- 
tity of  pure  silica.  The  whole  is  transferred  to  a  250  cc. 
Ehrlenmeyer  flask — rinsing  the  mortar  with  more  silica 
The  flask  is  weighed  and  a  weighed  quantity  of  concen- 
trated sulfuric  acid  is  added.  The  record  should  now 
show  the  weight  of  flask,  silica  and  acid.  The  flask  is 
gently  heated  and  the  loss  of  weight  is  calculated  as  sili- 
con fluoride. 

Iron.  For  use  in  light  colored  enamels  the  iron  con- 
tent of  the  fluorspar  is  important.  Five  grams,  finely 
ground,  are  heated  in  a  platinum  dish  with  an  excess  of 
sulfuric  acid  as  long  as  hydrofluoric  acid  is  given  off. 

After  cooling  it  is  diluted  with  100  cc.  of  water,  and 
after  reducing  by  drawing  through  a  Jones  Reductor  the 
solution  is  titrated  with  N/10  potassium  permanganate 
solution. 

Accurate  Method  for  Fluorine.  The  fluorine  may  be 
accurately  determined  by  the  following  method : 

One  gram  sample  (ground  to  pass  through  200  mesh 
sieve)  is  mixed  with  three  grams  silica  and  three  grams 
each  sodium  carbonate  and  potassium  carbonate  in  a 
platinum  crucible.  Heat  gradually  until  it  is  in  quiet 
fusion.  The  thin  liquid  fusion  soon  changes  to  a  thick 
paste  or  only  sinters  somewhat.  The  reaction  is  complete 
when  there  is  no  further  evolution  of  carbon  dioxide. 

After  fusion  the  melt  is  treated  with  water  and  after 
cooling  the  insoluble  residue  is  filtered  off  and  thoroughly 
washed.  The  solution  contains  all  fluorine  and  consider- 
able silica.  Remove  the  silica  by  adding  four  grams  solid 
ammonium  carbonate.  Heat  liquid  at  40°C.  for  some 
time  and  let  stand  over  night.  Filter  in  morning  and  wash 
with  ammonium  carbonate  water. 

Evaporate  on  water  bath  almost  to  dryness  in  plati- 
num dish  (keep  covered,  as  liquid  foams) .  Dilute  with  a 
little  water.  Add  a  few  drops  of  phenolphthalein.  Add 

96 


dilute  HC1  until  colorless.  Heat  on  steam  bath  and  color 
will  return.  Cool  and  repeat  operation  until  1.5  cc.  dou- 
ble normal  HC1  is  sufficient  to  make  colorless.  Remove 
last  traces  silica  by  treating  the  solution  with  a  solution 
of  moist  zinc  oxide  in  ammonia  water.  Boil  until  am- 
monia is  completely  expelled.  Filter  off  silica  and  zinc 
oxide  and  wash  with  water. 

Precipitate  fluorine  as  calcium  fluoride  and  calcium 
carbonate  by  adding  an  excess  of  calcium  chloride.  Filter, 
using  blue  ribbon  paper,  and  wash  thoroughly  with  hot 
water.  Dry  precipitate  on  funnel.  Transfer  as  much  as 
possible  to  a  platinum  crucible.  Burn  filter  and  add  ash. 
Ignite  contents  of  crucible. 

After  cooling  the  mass  is  covered  with  a  slight  excess 
of  dilute  acetic  acid  (this  changes  the  calcium  oxide  to 
soluble  acetate).  Evaporate  to  dryness  on  steam  bath. 
Take  up  with  water.  Filter,  wash  and  dry.  Transfer 
most  of  precipitate  to  weighed  platinum  crucible.  Burn 
filter  paper.  Add  ash.  Ignite  and  weigh  as  calcium 
fluoride  CaF2.  To  confirm  the  results  add  cautiously  little 
concentrated  sulfuric  acid.  Evaporate  off  excess  sulfuric 
acid,  ignite  and  weigh  as  calcium  sulfate. 

The  Analysis  of  Oxides  of  Antimony 

Arsenic.  One  gram  of  oxide  of  antimony  is  dis- 
solved in  10  cc.  of  strong  hydrochloric  acid — at  as  low  a 
temperature  as  possible.  The  solution  is  then  cooled  and 
packed  in  ice  and  the  arsenic,  which  is  almost  invariably 
present,  is  removed  by  passing  through  H2S  for  several 
hours.  The  As2S3  is  filtered  off  in  a  weighed  Gooch  cru- 
cible, washed  first  with  CS2  and  alcohol  then  with  concen- 
trated hydrochloric  acid  and  dried  at  100°,  and  weighed 
as  As2S3. 

Antimony.  The  filtrate  from  above  is  put  into  250  cc. 
volumetric  flask,  rinsing  the  beaker  well  with  concen- 
trated hydrochloric  acid  and  an  equal  part  of  water.  All 

97 


the  H2S  is  removed  by  passing  through  a  current  of  air. 
Five  grams  of  tartaric  acid  are  added  and  the  liquid 
diluted  to  the  mark. 

Twenty-five  cc.  of  the  solution  are  measured  out  with 
a  pipette  and  are  neutralized  with  dry  sodium  bi-car- 
bonate — keeping  covered  to  avoid  loss — finally  a  pinch  of 
sodium  bi-carbonate  and  a  cubic  centimeter  of  clear 
starch  solution  is  added  and  the  mixture  is  titrated  with 
N/10  iodine  solution. 

1  cc,  N/10  Iodine  =  0.0060  grams  Sb 

The  Analysis  of  Oxide  of  Cobalt 

Arsenic.  One  gram  finely  pulverized  sample  is  fused 
at  low  heat  with  ten  grams  bisulfate  of  potassium  for 
three  hours.  The  melt  is  extracted  with  water  acidified 
with  sulfuric  acid  and  the  arsenic  is  precipitated  from  the 
warm  acid  solution  with  H2S,  collected  in  a  weighed 
Gooch  crucible,  washed  with  water  containing  H2S  and 
dried  at  100°  for  one  hour  and  weighed  as  As2S3. 

Cobalt.  The  filtrate  from  above  is  boiled,  and  at  the 
same  time  air  is  drawn  through  to  remove  the  H2S,  and  it 
is  then  treated  by  Fisher's  Potassium  Nitrite  method1  to 
separate  the  cobalt  and  the  nickel. 

The  concentrated  solution  containing  salts  of  both 
metals  is  treated  with  pure  potassium  hydroxide  to  alka- 
line reaction,  made  slightly  acid  with  acetic  acid,  and  to 
this  a  concentrated  solution  of  pure  potassium  nitrite 
that  has  been  made  slightly  acid  with  acetic  acid  is  added. 
After  vigorous  stirring,  the  mixture  is  allowed  to  stand 
twenty-four  hours  in  a  warm  place.  Before  filtering,  a 
little  of  the  clear  solution  is  pipetted  off  and  treated  with 
more  potassium  nitrite  to  see  if  the  precipitation  of  the 
cobalt  has  been  complete.  If  a  precipitate  is  formed,  the 
whole  solution  is  treated  with  more  potassium  nitrite  and 
again  allowed  to  stand  until  complete  precipitation  is  ef- 

1Treadwell,  Vol.  II,  p.  180. 

*    98 


fected.  The  precipitate  is  then  filtered  and  washed  with 
a  barely  acid  5  per  cent  solution  of  potassium  nitrite  until 
1  cc.  of  the  filtrate,  after  being  boiled  with  hydrochloric 
acid  and  treated  with  caustic  potash  and  bromine  water, 
no  longer  gives  a  black  precipitate  of  nickelic  hydroxide. 
The  cobalt  precipitate  is  then  transferred  to  a  porcelain 
dish,  covered,  and  hydrochloric  acid  is  gradually  added 
until  there  is  no  further  evolution  of  nitric  oxide,  and 
after  filtering,  the  cobalt  is  precipitated  by  means  of  caus- 
tic potash  and  bromine  water. 

The  precipitate  is  filtered  off,  using  blue  ribbon  filter 
paper,  dried,  and  ignited.  After  cooling  it  is  treated  with 
water  in  order  to  remove  the  small  amount  of  alkali  which 
is  always  present,  after  which  the  residue  is  ignited  in  a 
stream  of  hydrogen  and  weighed  as  metal.  After  weigh- 
ing, the  metal  is  dissolved  in  hydrochloric  acid,  evapor- 
ated to  dryness,  the  dry  mass  moistened  with  hydrochlor- 
ic acid,  then  treated  with  water,  and  the  small  residue  of 
silicic  acid  is  filtered  off.  This  residue  is  ignited  and  its 
weight  subtracted  from  that  obtained  after  the  ignition 
in  hydrogen. 

Nickel.  The  filtrate  containing  the  nickel  is  treated 
with  hydrochloric  acid  until  the  nitrite  is  completely  de- 
composed, and  the  nickel  is  precipitated  with  potassium 
hydroxide  and  bromine  water  as  brownish-black  nickelic 
hydroxide  [Ni  (OH)3.] 

The  precipitate — which  seldom  contains  more  than 
ten  milligrams  of  nickel — is  washed  with  hot  water,  col- 
lected on  a  filter  and  is  dried,  ignited  separately  from 
the  filter,  and  weighed  as  NiO,  in  which  form  it  was  prob- 
ably present  in  the  oxide. 

Steel  Plate 

The  steel  best  adapted  for  enameled  ware  is  of  very 
low  carbon  value  and  extremely  low  in  the  other  impuri- 
ties, in  fact,  the  nearer  pure  iron  the  better.  Of  the  steel 


plate  used  by  the  Columbian  Enameling  and  Stamping 
Company,  the  best  satisfaction  was  obtained  from  those 
giving  the  following  analysis : 

Sulfur  from  .040%  to  .050% ;  phosphorous  from 
.030%  to  .090%;  silica  less  than  .01%;  manganese  from 
.060%  to  .040%,  and  carbon  less  than  0.10%.  The  sheets 
must  be  of  an  even  gauge  for  seamless  drawn  work  and  of 
a  dark  soft  quality,  which  allows  them  to  be  drawn  with- 
out tearing.  When  the  vessel  is  made  without  drawing  and 
sheets  are  used  flat,  this  evenness  of  gauge  is  not  so  much 
an  object.  The  grain  in  all  cases  must  be  as  open  as  pos- 
sible. The  sheet  must  be  low  in  carbon  and  sulfur,  as 
these  develop  gases  at  temperatures  of  the  muffle,  which 
would  cause  the  enamel  to  peel  off. 

Samples  of  the  steel  plate  are  obtained  from  drillings 
taken  from  eight  or  ten  sheets  stacked  in  a  pile,  and 
drilled  holes  are  run  every  two  inches  on  the  diagonal  of 
the  plate.  Drillings  are  sampled  down  to  twenty-five 
grams,  which  are  kept  in  stoppered  bottles.  The  method 
of  analysis  is  that  commonly  employed  by  steel-works 
chemists,  and  can  easily  be  found  in  print  elsewhere,  and 
for  that  reason  will  not  be  given  here. 


100 


ATOMIC  AND   MOLECULAR  WEIGHTS   AND 

FACTORS  USED  IN  CERAMIC  :    :  :•  --•-;-.: 
CALCULATIONS  i 

Aluminum, 

oxide,  A12O3  *  102.2  fR2O3  — 102 

hydrate,  A12O3.3H2O         156.3     R2O3  — 156 

1  Al— oxide      =   1.529  Al— hydrate 

=  6.536  Al— sulfate 
"  =:  8.893  Ammonia  Alum 

"  =1  2.534  China  Clay 

"  =  2.548  Cryolite 

=  9.305  Potash  Alum 
"  =  5.154  Soda  Feldspar 

=  3.069  Am.  Enamel  Clay 

Antimony, 

oxide,  Sb2O3  288.4  R2O3  — 288 

tetroxide,  Sb2O4  304.4  R2O3  — 304 

pentoxide,  Sb2O5  320.4  R2O3  —  320 

sulfide,  Sb2S3  336.6  R2O3  — 337 

1  Sb— trioxide  =  1.167  Sb— trisulflde 

=  1.111  Sb— pentoxide 

Arsenic,  trioxide,        As2O3  197.9     R2O3  — 198 


Barium, 

carbonate, 

BaCO3 

197 

.4 

RO 

—  197 

sulfate, 

BaSO4 

233 

.4 

RO 

—  233 

1  Ba  —  carb.                 = 

0.777 

Ba—  oxide 

1  Ba  —  oxide                = 

1.287 

Ba—  carb. 

1  Ba—  sulfate             = 

0.657 

Ba—  oxide 

Boric  Acid,       B2O3.3H2O  124.0     B203  —124 

(Fused),      B2O3  70.0     B2O3  —    70 

RO.2B2O3  — 382 
RO.2B2O3  — 202 


Borax, 

(Fused), 

Na2B4O7.10H2O     382.2     R( 
Na2B4O7                  202.0     R( 

1  Boric  Acid              =  0.548  B2O3 
1  B203                          =   1.771  Boric  Acid 
1  Borax                        =  0.529  Borax    Fused 
1  Borax                        =  0.162  Na—  oxide 
1  Borax                         =  0.366  B2O3 
1  Borax    (Fused)       =  0.307  Na—  oxide 
1  Borax           "             =  0.693  B2O3 
1  Borax           "             =  1.892  Borax 

1  Compiled  by  Robert  D.  Landrum,  mainly  from  Report  of  Committee  of  Equiva- 
lent Weights,  Transactions  of  American  Ceramic  Society,  Vol.  II,  pages  196  to  278. 
The  reader  is  referred  to  this  report  for  full  explanation  and  method  of  using  these 
equivalent  weights. 

*Molecular  Weight.     fEquivalent  Weight. 

101 


Cadmium  ^Ifide,        CdS  *144.5    tCdS    — 145 


carbonate,  CaCO«  100.1  RO  —100 

fluoride,  CaF2  78.1  RO  —    78 

oxide,  CaO  56.1  RO  —    56 

phosphate,  Ca3(PO4)2  310.3  RO  —103 

sulphate,  CaSO4.2H2O  172.2  RO  —172 

1  Ca — fluoride  =  0.718  Ca — oxide 

=  0.487  F. 

1  Ca— oxide  =  1.786  Ca— carbonate 

=   1.321  Ca— hydrate 
=  3.073  Ca— sulfate   (Gypsum) 

1  Ca — phosphate        =  0.542  Ca — oxide 


China  Clay,  Al2O32SiO2  R, 


•fCVj 

2H2O  258.0     2SiO2|  —  258 


Cerium 

dioxide,  CeO2  172.3     CeO2    — 172 

sesquiojdde,  Ce2O3  328.3     R2O3    — 328 

Chromate  of  Barium,  BaCrO4  253.5     2RO  1 

R2O3  j—506 

Chromate  of  Lead,      PbCrO4  323.1     2RO  ) 

R203  }— 646 

Chromium  Oxide,        Cr2O3  152.0     2RO   ) 

R203  I—  152 

1  Cr — oxide  =  1.658  Am — bichromate 

"  ==  2.001  Am — chromate 

"  =  1.828  Cr— hydrate 

=  5.261  Cr— nitrate 

=  4.710  Cr— sulfate 

=  6.288  Cr — ammonia  alum 

Cobalt 


carbonate, 

CoCO 

3 

119 

.0 

RO 

—  119 

chloride, 

CoCL 

.6H2O 

238 

.0 

RO 

—  238 

nitrate, 

Co  (NO 

*M 

5H2O 

291 

.1 

RO 

—  291 

oxide, 

Co203 

166 

.0 

RO 

—    83 

oxide, 

CoO 

75 

.0 

RO 

—    75 

oxide  (blk.), 

Co3O4 

241 

.0 

RO 

—    80 

sulphate, 

CoSO4. 

7H20 

281 

.2 

RO 

—  281 

i 

Co  —  carbonate         = 

0.630 

Co  —  ous 

oxide 

i 

Co  —  chloride            = 

0.315 

Co  —  ous 

oxide 

i 

Co  —  nitrate              = 

0.258 

Co  —  ous 

oxide 

i 

Co—  ic 

oxide 

— 

0.904 

Co  —  ous 

oxide 

i 

Co  —  ous  oxide         = 

1.587 

Co  —  carbonate 

it 

— 

3.173 

Co  —  chloride 

J 

M 

— 

1.173 

Co  —  ic  oxide 

( 

n 

— 

3.749 

Co—  sulfate 

*Molecular  Weight.     fEquivalent  Weight. 

102 


Copper 

oxide  (red)  Cu2O  *143.1   fRO  —    72 

oxide  (black)  CuO  79.6     HO  —    80 

sulphate,  CuSO4.5H2O  249.7     RO  —  250 

1  Cu— oxide  (Blk.)  =  0.899  Cu— oxide   (Red) 

1  Cu— oxide  (Blk.)  =  3.137  Cu— sulfate 

1  Cu— oxide  (Red)  =  1.112  Cu— oxide   (Blk.) 

1  Cu— sulfate  =  0.319  Cu— oxide  (Blk.) 

Cornwall  Stone,  IRQ  .  2.5  A12O3 

20.SiO2  1550.0  1RO1 

2.5  R2O3f  1550 
20.0  SiOJ 

Cryolite  Na7AlF6  210.0     3RO  \ 

A1203J— 420 

Feldspar  (Soda)          Na2O .  A12O3      524.0     IRQ   1 

6SiO2  1R2O3J — 524 

6SiOj 

Feldspar  (Lime-Soda)CaO)    A12O3     520.0     IRQ  1 

Na2O)  5SiO2  1R2O3  —  520 

5SiO2  J 

Feldspar  (Potash)       K2O.A12O3        557.0     IRQ  1 

6Si02  lR203U-557 

6SiO2J 

Ferric  Oxide  Fe2O3  159.7  R2O3  — 160 

Ferrous  Sulphide  FeS  87.9  R2O3  —176 
Ferric  Oxide 

(Magnetic)  Fe3O4  231.5  R2O3  —155 

Ferrous  Sulphate  FeSO4.7H2O  278.0  R2O3  —556 

Lead  Acetate  Pb  (C2H3O2) 2 

3H2O  379.2     RO      —379 

carbonate  (basic)  2(PbCO3) 

Pb  (OH)  2  775.3     RO      —258 
oxide  (red)  Pb3O4  685.3     RO      —  228 

Litharge  PbO  223.1     RO      —222 

Magnesium 

carbonate  MgCO3  84.3     RO      —    84 

oxide  MgO  40.3     RO      —    40 

1  Mg— carbonate       =  0.479  Mg— -oxide 

1  Mg — oxide  =  2.089  Mg — carbonate 


*Molecular  Weight.    tEquivalent  Weight. 

103 


Manganese 

carbonate 
di-oxide 

MnCO, 
MnO/ 

;•          *114.9 

86.9 

RO 

—  115 

—    87 

Nickelic  Oxide 

NiO 

74.7 

RO 

—    75 

Nickelous  Oxide 

Ni203 

165.4 

RO 

—    83 

Nickel  Sulfate 

NiSO4. 

7H2O      280.9 

RO 

—  281 

i 
i 
i 

Ni208 

NiO                   = 
NiO                    = 

:   0.903  NiO 
:   1.107  Ni2O3 
:  3.760  Ni—  sulfate 

Potash  Alum  K2SO4A12  (SO4) , 

RO 
24H2O  949.1  A12O3  —949 


Potassium 

antimonate 

RO 

KSbO3 

207.3  Sb2O5  —414 

bichromate 

K2Cr207 

294.2     RO    )— 
2R2O3j—  294 

carbonate 

K2CO3.2H2O 

174.2     RO     —  174 

carbonate 

(calcined) 

K2C03 

138.2     RO     —  138 

nitrate 

KN03 

101.1     RO     —202 

1  K— nitrate  =  0.466  K— oxide 

=  0.683  K— carbonate 

"  =  0.737  K— chloride 

=  0.863  K— sulfate 

1  K— oxide  =  1.467  K— carbonate   (anhydrous) 

"  =  1.848  K— carbonate    (crystal) 

=  1.582  K— chloride 

=  1.192  K— hydrate 

"  =  2.145  K— nitrate 

=  1.849  K— sulfate 

"  =  5.927  K— feldspar 

"  =  10.066  K— alum 

Selenium  Se  79.2     SeO2  —    79 

Oxide  SeO2  111.2     SeO2  —111 

Silica  Si02  60.3     SiO2   —    60 

*Molecular  Weight.     fEquivalent  Weight. 

104 


Sodium 

antimonate 
carb.  (cryst.) 

carb.  (soda  ash) 
chloride 
hydrate 
nitrate 
silico  fluoride 


NaSb03 

*  191.2  tROSb205— 

382 

Na2CO3. 

10H2O  286.2     RO     — 

286 

Na2CO3 

106.0     RO     — 

106 

NaCl 

58.5     RO     — 

117 

NaOH 

40.0     RO     — 

80 

NaNO3 

85.0     RO     — 

170 

Na2SiF6 

188.3  ROSiF6    — 

189 

1  Na  —  carbonate 

(crystals) 

=  0.371 

1  Na  —  carbonate 

(crystals) 

=  0.216 

1  Na  carbonate 

2.698 

(anhydrous) 

=  0.585 

1  Na  carbonate 

0.531 

(anhydrous) 

=  0.774 

1  Na—  chloride 

=   0.365 

1  Na—  hydrate 

=  6.161 

1  Na—  nitrate 

=  3.258 

1  Na2O 

=  4.613 

" 

=   1.710 

« 

=   1.887 

« 

=   1.290 

" 

=  2.742 

" 

=  5.193 

" 

=  2.290 

" 

=  8.500 

=  0.371  Na — carbonate   (anhydrous) 

Na2O 

Na — carbonate  (crystal) 

Na20 

Na2O 

Na20 

Na2O 

Borax  (crystal) 

Borax  (anhydrous) 

Na — carbonate    (crystal) 

Na — carbonate   (anhydrous) 

Na— chloride 

Na— hydrate 

Na— nitrate 

Na— sulfate   (crystal) 

Na — sulfate    (anhydrous) 

Na — feldspar 


Strontium 

carbonate 
sulfate 

Tin 

chloride 
oxide 

Titanium  Oxide 


SrCO3 
SrSO4 

SnCl2.2H2O 
SnO2 

TiO2 


147.6  RO  —148 

183.7  RO  —184 


226.0     RO  —226 
151.0     RO  —151 

80.0     TiO,—    80 


Uranium 

oxide 

oxide  (com'l) 


Zirconium  Oxide 


U02 

Na2O.U2.O( 

6H2O 


ZrO2 

"Molecular  Weight.    tEquivalent  Weight. 

105 


270.5  R2O3—  543 

746.0  RO  I 

R2O3J—  746 

122.6  ZrO,  —  123 


CUBICAL  COEFFICIENT  OF  EXPANSION 

in    Millimeters    per    degree    Centigrade,    as    determined 
by  Winkelmann  and  Schott  and  Mayer  and  Havas 

(See  Sprechsaal  1911,  No.  13) 


A1F3 

=  4.4  X  10~7 

MgO 

=  0.1  X  10-7 

A1203 

=  5.0  X  10-7 

MnO 

=  0.1  X  10-7 

As205 

=  2.0  X  10~7 

Na3AlF 

6  =  7.4  X  10-7 

BaO 

=  3.0  X  10-7 

NaF 

=  7.4  X  10-7 

BeO 

=  4.7  X  10-7 

Na2O 

=10.0  X  10-7 

B208 

=  0.1  X  10~7 

NiO 

=  4.0  X  10~7 

CaF2 

=  2.5  X  10~7 

PbO 

=  4.2  X  10~7 

CaO 

=  5.0  X  10~7 

P205 

=  2.0  X  10~7 

CeO2 

=  4.2  X  10~7 

Sb205 

=  3.6  X  10~7 

CoO 

=  4.4  X  10~7 

SiO2 

=  0.8  X  10-7 

Cr203 

=  5.1  X  10-7 

SnO2 

•=  2.0  X  10~7 

CuO 

=  2.2  X  10~7 

ThO2 

=  6.3  X  10-7 

Fe203 

=  4.0  X  10~7 

TiO2 

=  4.1  X  10~7 

K2O 

=  8.5  X  10-7 

ZrO2 

=  2.1  X  10~7 

Li02 

=  2.0  X  10-7 

ZnO 

=  1.8  X  10~7 

106 


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